Gold in the Pottery IndustryTHE HISTORY AND TECHNOLOGY OF GILDING PROCESSES

L. B. HuntJohnson Matthey & Co. Limited, London

The gilding of porcelain has been practised from the earliest days of its

production, the permanente and brightness of gold naturally appealing

to designers and manufacturers. Nowadays some five tons of gold are re-

quired annually for the decoration of porcelain and earthenware, and

this article recounts the developments in gilding from the early closely

guarded secret recipes to the current techniques involving not only some

very complex organic chemistry but also a considerable degree of in-

genious mechanisation of the processes, although the role of the skilled

hand gilder is still in evidente on more expensive productions.

The gilding of porcelain and pottery — rangingfrom the simple edging on a plate to the elaboratelydecorated vase with richly gilt panels and scrolls —has always been a prominent feature. It is more than250 years since the introduction of chemical methodsof preparing gold in a powder form suitable for ap-plication to porcelain led to the replacement of the oldprocedure, used first in China, of simply applyinggold leaf over a layer of linseed oil and litharge, orwith egg white or shellac. It is 150 years since the firstgold preparátion in liquid form was devised, bringingwith it the much wider and more economical use ofgold in the pottery industry.

The history of these developments is one of jealous-ly guarded secret recipes with the supposed secretsoften being spread by the migration of skilled workersfrom one factory to another. On occasion, however,there were major contributions from one or twodistinguished scientists.

Johann Friedrich Böttger1685-1719

The thousand year old secret of Chinese porcelain was re-discovered by Böttger, a young apothecary and alchemistwho had fled from the court of King Frederick I of Prussiaonly to be imprisoned in Dresden by Augustus the Strong,Elector of Saxony, an assiduous collector of china. At firsthe was commanded to make gold from base metals, but in1707 his master ordered him to attempt the production ofporcelain. He then placed over the doorway of hislaboratory a notice:

'God our creator has turned a gold maker info a potter'.

He produced the first unglazed porcelain in 1709 and in thefollowing year the famous Meissen factory was established.Worn out by his exertions and his hardships, however,Böttger died at the early age of 34 before a really successfulmethod of gilding had been developed

The preparations in use today fall into three maingroups. Modern liquid golds are formulated from anorgano-gold compound containing a sulphur linkage,such as a gold sulpho-resinate or thiolate. The addi-tion of small amounts of other metals, includingbismuth, chromium, vanadium and rhodium, also astheir sulpho-resinates or similar compounds, isnecessary to secure both good adhesion of the goldfilm to the glaze and stability during the firing opera-tion, while•• the solvents comprise either natural orsynthetic materials — essential oils, chlorinated cyclic

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A Meissen plate, one of atravelling tea-set, made inabout 1730 and now in theBritish Museum. This is oneof the earliest examples ofthe high quality of firedgilding introduced there

hydrocarbons or glycol esters, with resins such asglyceryl abietate. The basic organic gold compoundsare extremely complex and of very high molecularweight.

Secondly, the older types of preparation in powderform are still relied upon extensively for heavier andmore expensive gilding, while the third group con-sists of preparations containing the gold in solutionbut with the addition of a proportion of gold inpowder form to provide the so-called liquid burnishgolds or matte golds.

The First European PorcelainTo return to the earliest days of European

porcelain; when Johann Friedrich Böttger, virtuallyimprisoned by the Elector of Saxony, finally succeededin 1709 not only in finding the right materials for theporcelain body but in building a kiln capable ofgiving him a temperature high enough to fire his ware,he naturally began to turn his mind towards itsdecoration. In the first few years, gilding was carriedout by the old method of applying gold leaf by meansof a lacquer, without firing, but this was of courseeasily abraded so that very few examples havesurvived.

Where then did Böttger turn to find a reliablemeans of gilding? There was in fact open to him oneexcellent source of information on the likely aspects

of gold chemistry. Böttger, born in Schleiss in Saxonyin 1685, was apprenticed at the early age of 12 to anapothecary named Zorn in Berlin, and at night he in-dulged his alchemical ambitions in the apothecary'slaboratory. In these experiments he was encouragedby a much older man, Johann Kunckel, a friend of theZorn family who was often in their house. As well asbeing something of an alchemist Kunckel was themost advanced chemist of the seventeenth centuryand a prolific writer of text books. (Curiously he hadearlier been in the service of Johann Gregor II, Elec-tor of Saxony, the grandfather of Augustus theStrong, Böttger's autocratic employer). Kunckel hadpublished in 1679 his `Ars Vitraria Experimentalisoder Vollkommene Glasmacher-Kunst, a complicatedwork based initially on the `L'Arte Vetraria' of theFlorentine priest Antonio Neri, written in 1612, andtranslated .into. English and dedicated to Robert Boylein 1662 by Christopher Merrett, who appended anumber of observations of his own. Kunckel's book-was in effect a German translation of these two works,followed by a lengthy section of his own, and it was inthis latter part that he included a chapter on thegilding and enamelling of glass which he reproducedfrom an unknown work, the author of which, he says,`had himself been a good glass painter, according tohis information had recently died, but of unknownname except that he wrote as H.I.S.'.

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In the course of this chapter, no less than sixteenrecipes were given for the gilding of glass, most ofthem describiing merely the sticking on of gold leaf,but a few involving heating the gilded ware in a coalfire 'so it never comes off .

It is a fair assumption that Böttger was well awareof this book and almost certainly possessed a copy ofhis own. But by the time he was wrestling with .theproblem of gilding in a more reliable way, a furtherwork of Kunckel's became available. This was his`Laboratoria Chymica', published in Hamburg andLeipzig in 1716, some thirteen years after theauthor's death but happily coinciding with Böttger'sneeds. Here, among other observations on the

Johann Gregorius Höroldt1696-1775

Sometimes referred to as the father of European porcelaindecoration, Höroldt was bomn in Jena, the son of a tailor.In 1718 he entered the newly established porcelain factoryin Vienna but two years later left for Meissen, together withSamuel Stöltzel (who had escaped from Meissen with hissecrets in 1719 but returned dissatisfiedl and who recom-mended him as `a well trained and experienced decorator'.His remarkable talents quickly enabled him to prepare acomplete palette of enamel colours and to devise a reliablemethod of gilding that was used for very many years. Thisportrait is from an etching by C. W. E. Dietrich made in1731 and preserved at Meissen

chemistry of gold, Kunckel described the precipita-tion of gold powder by the addition of a solution offerrous sulphate to a solution of gold in aqua regia togive `a quite beautiful and very fine precipitate'. Itwas this form of gold powder that was to put Böttgerand his successors at Meissen in a position toestablish a sound procedure for the gilding ofporcelain. Although, as wilt be seen, quite differentmethods were adopted in other porcelain factoriesfrom time to time, the ferrous sulphate precipitate re-mained for over two hundred years the basic startingmaterial in England as well as in Germany, and is stiltused to some extent in the preparation of modernburnish golds.

Johann Gregorius HSroldtAlthough Böttger had succeeded in gilding his

porcelain with Iightly fired gold, and had outsidedecorators carry out gilding by the methods of theglass workers, he did not see really durable gold ap-plied to his porcelain before his untimely death in1719. It was not in fact until about 1723 thatreasonably good gilding became a feature of Meissenporcelain, and for this the credit must be given to

The opening paragraph ofChapter XII of Höroldt'snote-book, compiled in 1731.The title reads 'How the Goldis to be Dissolved andPrecipitated' and goes on todetail the procedure fordissolving Dutch ducats inaqua regia and precipitatingthe gold with a solution offerrous sulphatePhotograph by courtesy of theArchive Department of the NationalPorcelain Factory, Meissen

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Johann Gregorius Höroldt, who arrived at Meissenfrom Vienna in 1720 as a young painter andenameller. It is likely that Höroldt found somemanuscript notes of Böttger's dealing with his at-tempts to produce enamel colours and gold decora-tion, although nothing of this kind has survived, butin any case, and in a most remarkable way, Höroldtsoon acquired a sound knowledge of contemporarychemistry, sufficient at least for him to develop arange of enamel colours and a procedure for gildingthat helped to create the full artistic flowering ofdecoration on European porcelain.

In 1731 the administrators of the Meissen factoryasked Höroldt and his tolleagues to put on record therecipes for their palette, and the small parchmentnote-book he compiled at this time is preserved in thearchives there. Dated December 24, 1731, the note-book entries are introduced with this sentence:

'True and correct description of enamel or vitrifiable colourswhich I have invented with God's help and which are used bythe local porcelain factory, also the gold and silver decorationand how such have to be treated'.

In the section on gilding, Chapter XII, running tosome ten pages and headed 'How the Gold is to beDissolved and Precipitated', Höroldt begins:

`One takes two ducats, the Dutch are the best, they are Basierto cut and also the aqua regia attacks the gold better'.

He chose well, because at that time the Dutch ducathad the highest gold content of any coinage inEurope, 23 7/8 carat, or 98.6 per cent. The solution ofthe ducats was then to be poured slowly into a filteredand diluted solution of 'Hungarian vitriol' (ferroussulphate), stirring with a clean quill to avoid the for-mation of larger particles of gold. The precipitate,.separated by decantation with hot water and thendried, was thoroughly mixed with a finely groundlead silicate flux and applied to the ware. The golddecoration was fired before the colours were appliedand finally burnished with pieces of flint.

After decorating with colours, the gold naturallybecame dull and had to be burnished again, butHtiroldt emphasises that the first polishing was stillnecessary to make the gold `even more beautiful'.

This then was the basis of the brilliant gilding thatcharacterised early Meissen porcelain, the golddecoration betoming more elaborate by about 1740.But the Seven Years' War brought to an end thedomination of Meissen, and when Frederick theGreat of Prussia occupied Dresden in 1762 he tookthe moulds and models, together with some of theleading workers, to the Berlin Porcelain factory whichhe then purchased for himself. Undoubtedly the sameprocedure for gilding was used in Berlin and anumber of smaller factories established in Germany

as well as in the Vienna factory that had been set up in1717 with the help of two runaway workers fromMeissen and where Samuel Stöltzel, Böttger's kilnmaster at Meissen, spent a year in 1720 until hisreturn to Meissen bringing Höroldt with him. One ofStöltzel's recipe books has also survived and includesa description, rather less precise than Höroldt's, ofthe dissolution of gold and its precipitation with fer-rous sulphate.

Gilding at Vincennes and SèvresA very different approach was adopted in the early

years of porcelain production in France, and thereseems to have been no knowledge of the precipitationtechnique so successfully employed in Saxony. Asearly as about 1690 a type of porcelain was beingmade at St Cloud, and there is a well known referenceto the successful gilding of the ware in a book writtenby Dr. Martin Lister, later physician to Queen Anne,in the course of his visit to Paris with the Duke ofPortland in 1695:

`I saw the potterie of St Clou with which I was marvellouslywell pleased ... They had arrived at Burning on Gold in neatChequer Works'

This extraordinarily early record of 'burning on' thegold was not however the truc gilding process that weare considering here but merely involved applyinggold leaf with an iron tool as used by book binderswith the aid of a kind of gum made from quince seedsand then passing the ware through the kiln again.

The second porcelain factory to be set up in Francewas at Chantilly in 1725 under the patronage ofLouis-Henri de Bourbon, Prince de Condé, with oneCiquaire Cirou who had earlier worked at St Cloud,but the major development was of course theestablishment of the Vincennes porcelain works in1738 when Orry de Fulvi, brother of the Controller-General of Finance to Louis XV, secured the servicesof Gilles and Robert Dubois from Chantilly andthrough his brother's influence obtained the use ofbuildings attached to the Chateau de Vincennes. TheDubois brothers were unsuccessful and were shortlydismissed and replaced by Francois Gravant, alsofrom Chantilly. Gravant brought with him a recipefor gilding which, although not altogether successful,formed the basis of French gilding technique for verymany years. Gold leaf was to be ground to powder ona slab with fine starch and a very little white of egg,well washed with water several times and then dried.To apply the gold to the porcelain a mordant of eithergum or a mixture of fine sand and litharge was used.

By 1745 a successful `soft-paste' porcelain wasbeing produced, and a monopoly was obtained fromLouis XV for the manufacture of porcelain after thestyle of Meissen, forbidding any other establishment

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to be set up for the making of porcelain and alsorestricting the use of gilding to Vincennes. Orry deFulvi was not, however, satisfied with the gildingtechnique and in 1748 he purchased a `secret formula'from Brother Hypolite, a Benedictine monk in thepriory of St Martin des Champs in Paris, for the largesum of three thousand livres in cash and an annualpayment of six hundred livres.

Jean Hellot and the Monk's Secret FormulaThe factory was now in financial difficulties, and

the king's mistress, Madame de Pompadour, herselfgreatly interested in porcelain and anxious to en-courage its production under her own patronage, per-suaded Louis to invest heavily in the enterprise, andeventually to take control, the factory then betomingthe Manufacture Royale de Porcelaine.

In 1751 Orry de Fulvi died and a number of newappointments were made, the most important fromour present point of view being that of Jean Hellot aschemist. Hellot (1685-1766) was one of the foremost

A blue vase and cover made at Vincennes in about 1750 andnow in the British Museum. It is thickly decorated withgold, but by a technique entirely different from that usedat Meissen, giving a slightly softer and yellower tone.

chemists of his time, a member of the AcademieRoyale des Sciences since 1735 and twice its Directorin 1751 and again in 1764, elected a Fellow of theRoyal Society of London in 1740, and a scientific ad-viser to the government on dyeing, on chemistry andmetallurgy, and the author of a number of works onassaying, on mining and metallurgy and on dyestufls.He immediately set out to study and improve thecolours and glazes at Vincennes, and he was equallyquick to investigate the gilding recipe of BrotherHypolite, referring disparagingly to the large amountof money paid `for his supposed secret. It is he who isin charge of the wine, he's very stupid'.

Hellot's note-books are fortunately preserved in thearchives at Sèvres, to where the factory was removedin 1756, a site selected by Madame de Pompadournear her chateau, and contain, among many otherrecords of his work on new colours, an account of hislengthy investigations on gilding (1). After complain-ing that Orry de Fulvi had erroneously copiedHypolite's formula, he goes on to give `the true andverified secret of Brother Hypolite's painting gold',which was recorded after he had visited on several oc-casions during 1751 the Priory of St Martin desChamps to watch Hypolite carry out his process.

First, gold leaf was to be ground on a large por-phyry slab or a real turtle shell for some ten or twelvehours in a thick solution of gum arabic in water untilreduced to a fine powder, which was to be washedwith hot water, then passed through a fine sieve anddried. The `secret' mordant was then to be preparedby distilling white vinegar over a number of.. rgeonions and garlic cloves: Finally the gilders were to.take a little of the gold powder, mix it on a shell withthe right amount of the mordant, and apply it with abrush. The decoration was allowed to dry beforebeing fired, and was then burnished.

The idea of employing garlic in the mordant, by nomeans new or secret, is extremely interesting in thatone of its major constituents is a sulphur-containingessential oil, and to this day the successful compoun-ding of gold preparations for porcelain and potteryhinges upon the presente of a sulphur linkage to thegold atom. However, recipes using garlic in mordantsfor the gilding of glass and other materials can betraced back at least to fifteenth and sixteenth centurymanuscripts, copies of which might well have beenavailable in the library of St Martin des Champs.

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There are subtle but perceptible variations in the ap-pearance of the gilding on porcelain, largely dependentupon the size and shape of the gold particles used. Toillustrate the essential differences in procedure at Meissenand at Vincennes and Sèvres, laboratory reproductions oftheir formulae were carried out in the Johnson MattheyResearch Centre. These scanning electron micrographs, ata magnification of 1000, show the gold preparations afterfiring but before burnishing.

Top: Gold powder precipitated from solution in aqua regiaby ferrous sulphate, as practised in the early years atMeissen. The rather coarse round particles gave asomewhat duller appearance than later techniques

Centre: At Vincennes and later at Sèvres, gold leaf waslaboriously ground up in honey, a viscous medium simplyused to avoid the particles adhering to one another. Thehoney was then washed away and the gold well driedbefore applying to the porcelain with a mordant. The flatparticles produced in this way gave the gilding a softer andslightly more yellow appearance

Bottom: About 1780, a very different and less expensivemethod was adopted at Sèvres. Gold was precipitated fromits solution in aqua regia by adding a solution of mer-curous nitrate, this method yielding a very much finer andmore flocculent precipitate than ferrous sulphate. Theresultant gilding was thinner, less durable and tendedto show a rather brassy appearance

Cennino d'Andrea Cennini's `Il Libro dell'Arte, forexample, compiled in Florence just after 1400,describes a mordant for gilding with garlic bulbs,while the `De Secreti' of Allessio Piemontese, writtenin Venice in 1555, also contains a recipe for gildingusing gold leaf ground up in honey with a mordantbased upon garlic and vinegar.

None the less, Brother Hypolite's formula was inuse for a long period for the superti and lavish gildingat Vincennes and Sèvres, the monk himself preparingthe gold and the mordant, but honey was eventuallysubtituted for the gum arabic as the viscous mediumin which the gold leaf was ground.

Compared to Meissen gilding — on a true hard-paste porcelain — this procedure was successfulenough, and probably essential on the soft-paste ofSèvres as it needed only a relatively low firingtemperature. A slight but perceptible difference canbe discerned between the gilding on Meissen andVincennes or early Sèvres porcelain, the latter beingslightly more yellow and softer in texture. The elec-tron micrographs on this page clearly show thedissimilarity in the shape of the •gold powders used.

True hard-paste porcelain was not made at Sèvresuntil 1772, the necessary research owing a great dealto another famous chemist, Pierre-Joseph Macquer(1718-1784), who had joined Hellot as his assistant in

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1757 and had succeeded him two years later. Thisposed the problem of finding a new method ofgilding, and the new director, Melchior-FrancoisParent, also appointed in 1772, concerned too at thehigh cost of the older method, sought for an alter-native. By this time the ferrous sulphate precipitatehad become known in France, and Parent, in amemorandum preserved in the archives at Sèvres,wrote that `gold dissolved and precipitated from aquaregia is always more attractive and has a brightercolour' but was less ductile and, compared with theexisting procedure, consumed more gold for a givennumber of pieces of porcelain. He proposed a methodemployed by metal gilders, dissolving gold in mer-cury — which had first to be carefully purified —evaporating the excess mercury and separating theamalgam in nitric acid to leave a fine gold powder.

The gilders very soon objected to this method, part-ly because of the danger to their health in evaporatingthe mercury but also because of the high cost com-pared with the precipitation method and the less at-tractive appearance of the gilding. In a memorandumsubmitted to the management, they insisted that withtheir then existing method, presumably a precipita-tion, the gold was much finer, presented no dif-ficulties in use and gave a perfect appearance on hardporcelain, while they maintained that for softporcelain (which continued to be made alongside thenew hard body until 1804) neither a precipitated goldpowder nor one made with mercury would ever besuitable and that the old technique of grinding goldleaf was essential.

The Mercurous Nitrate MethodHowever, a still further procedure was soon to be

adopted for hard-paste porcelain. If instead of using asolution of ferrous sulphate one of mercurous nitrateis employed, a much finer and more flocculentprecipitate is obtained, while a small amount of mer-cury compound is occluded in the gold powder, a fac-tor that assists materially in securing good adhesionand in reducing to some extent the temperature offiring. The date of the inception of this method isdifficult to establish with accuracy, but a valuableclue is contained in a memorandum dated 1781 fromJean-Jacques Bachelier — a protégé of Madame dePompadour who was artistic director for over fortyyears — to the Comte d'Angiviller who had succeededParent as director at Sèvres in 1778 when the Jatterwas imprisoned for misappropriating funds.Bachelier refers to the great expense of the enormousquantity of gold being used, and to the poor taste ofsome of the gilding, and goes on:

`There are only two methods of gilding porcelain. Shouldthere not be a third? We have some good ideas on this possibili-ty: there are interesting experiments to be made' (2).

It can be assumed then that sometime in the middeof the 1780's this new method was adopted at Sèvres.The precipitated gold, well washed of course anddried, was used with a mixture of bismuth oxide,borax and turnpentine to assist in adhesion to theharder glaze. The greater degree of fineness of thegold particles precipitated in this way is clearly shownin the electron rnicrograph on page 121.

This was the preferred method used for very manyyears on hard porcelain at Sèvres. Some sixty yearslater, Alexandre Brongniart, the scientist appointedas director by Bonaparte in 1800, wrote that this wasthe method generally employed and that, althoughcompared with the ferrous sulphate precipitate it wasmore economical and gave a much finer powder, itdid not withstand usage so well and often a double ap-plication, with burnishing before and after the secondtreatment, was found necessary (3).

The ferrous sulphate precipitate, however, yieldeda more solid appearance to the gilding despite theexpense of the considerably greater quantity of goldused. Brongniart adds an amusing note on the pro-duction of imitations of very old Sèvres porcelain bythe addition of traces of copper to the honey-groundgold `to give a dull appearance to the gilding whichamateurs attribute to the antiquity of the piece'.

The Factories at Limoges and TournaiAfter the introduction of hard-paste porcelain at

Sèvres the restrictions on others and the prerogativeon the use of gold were gradually relaxed, and anumber of porcelain factories blossomed forth inFrance, several of them under the patronage of thenobility, anxious to associate themselves withporcelain man(ufacture. One of the earliest was atLimoges, under the protection of the Comte d'Artois,and first followed the Sèvres procedure, grinding inhoney and applying the gold to the ware with boraxand gum water, but later adopted the ferrous sulphateprecipitation method with a bismuth oxide and boraxflux mixed with turpentine to give a brighter andmore lavish effect. By about the middle of the nine-teenth century, however, this method was graduallyreplaced by the mercurous nitrate precipitate to give abriljant effect with greater economy (4).

Similarly the eldest son of the Comte, the Ducd'Angoulême, sponsored a porcelain factory in Parisin 1780 with Christophe Dihl as colour chemist.They were quick to profit from the removal of theban on gilding imposed by Sèvres, and they were tohave an influence on the techniques adopted by thefamous Worcester factory in England.

Before this, however, an important factoVy hadbeen established at Tournai in Belgium and.was pro-ducing soft-paste porcelain by 1751. Tournai was suf-ficiently remote from Paris to be able to ignore the

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prohibition on gilding, and its porcelain displayedthick and rich gilding, almost certainly by means ofthe early procedure used at Vincennes and Sèvres, thegrinding of gold leaf in honey. One of the importantfeatures of Tournai, however, was its link with theChelsea factory in London, founded in about 1743 byNicholas Sprimont, a goldsmith from Liège, andCharles Gouyn who was a Huguenot and a jeweller.For some years the little gilding used was rather dullin appearance, but by around 1758 a beautifully softtype of gilding made its appearance, resembling thatof both Sèvres and Tournai.

This thick soft gilding, equal to the best of con-tinental work, continued to characterise the wares forsome time after the Chelsea factory was purchased byWilliam Duesbury of Derby in 1770.

Josiah Wedgwood's; DifficultiesThe early difficulties encountered and solved by

the great Josiah Wedgwood are indicative of theuncertainties of gilding methods. Wedgwood set upfor himself in Staffordshire in 1759, when only 29years old, to make earthenware, both useful and or-namental, and his much improved product was soonsuccessful. By 1765 he received his first order fromRoyalty, for `a complete sett of tea things, with a goldground and raised flowers upon it in green' fromQueen Charlotte, the wife of King George III. In aletter to his brother John in London dated June 17,1765, he wrote:

`I have just begun an Enamel work, and am in great want of.some gold powder such as is burnt in upon China. It is madeby one Mr. Shenton (only) and sold by him at 7 guineas Per oz.Mr. Giles Enameller in Berwick St Soho can teil you whereMr. Shenton lives, which is the best Direction I can get. Ishould be glad to have a few pennyweights by way of tryal; if itanswers well shall want large quantities. Mr. Shenton mayperhaps give you instructions about the best manner of usingit. What I would be glad to know ... is whether she expects thegold to be burnt in, as it is upon the Chelsea china, or securedwith a varnish only, like the Birmingham waiters'.

About a month later, in another letter to brotherJohn, he wrote:

`I am very busy every day preparing sprigs, handles ..., mak-ing experiments in burning on gold etc., etc. for the service,and from experience I can tell you that the sooner I do 'em themore imperfect they will be.. . Powder gold would do them forme if I knew how to polish it after it is burnt. There is oneJinks who was a gilden in enamel at the Chelsea works and isnow at the Bow China work; if it would not be too tedious Iwish you would buy a cream colour enamelled cream Ewer andget Jinks to gild all the spaces but the flowers, etc. and burnthe gold in, by which you'll see if he is capable of doinganything for me'.

And again, in a post-script to a letter of August 7

`I have succeeded the first tryal in making powder gold which Ihave allways been told one man only in England could make,and desire you'l send me an oz of pure gold either in Ducats orgram or some form, send the powder too' (5).

Naturally enough, Wedgwood being the practicalscientist he was, he very soon solved his problems,and a few years later his `Commonplace Book' in-cludes a short recipe:

`Gilding on Porcelain — 10 parts of Gold powder, and 1 ofceruse — with gum water — Burnt in then Polish with Agate,rubbing always one way'.

By the 1780's his note-books reveal that he was fullyaware of all the variations on the gilding process andmaking use of them.

Gilding on British PorcelainThe porcelain factory with the Iongest continuous

history in England, the Worcester Royal PorcelainCompany, founded in 1751, likewise used gold leafground up in honey, washed, dried and applied with aflux, to produce an elegant and thick type of gildingin its earlier period under the famous Dr. Wall. In1783 the factory was purchased by its London agentThomas Flight, and a few years later, after a visit byhis son John to the Duc d'Angoulême's factory inParis, a quite different and more economical techni-que was adopted. This consisted in preparing anamalgam.of mercury with 'brown gold', (the ferroussulphate precipitate, sometimes purchased from thegold refiners), grinding this in turpentine with aglassy flux or with bismuth oxide and applying themixture to the ware. At a conveniently low firingtemperature the mercury was driven off and a mattgold resulted that could be burnished to give a richand brilliant effect.

This easier and cheaper method of gilding was usedby a number of British potteries in Staffordshire andelsewhere for many years until the development ofthe more scientifically compounded preparations ofthe last quarter of the nineteenth century. One or twotypical recipes confirm the procedure. At the Spodefactory in Stoke-on-Trent, for example, whereporcelain manufacture began in about 1800 and stillcontinues, the note book kept by the decorator HenryDaniel records the following recipe under the date1816:

New Gold Made out for Mr. Hancock`Dissolve an Ounce of Gold in Aqua Regia, precipitate with aStrong Solution of Copperas [ferrous sulphate] as filtered —then wash your precipitate of Gold well then dry it. Whendried pour upon it some Spirits of Salts to take the Iron outshould there be any then wash it well again. Dry it perfectly,then to the Ounce of Gold add 15 pennyweights of Quicksilverand 20 grains of Magister of Bismuth. Grind for use'.

A slightly more picturesque recipe preserved in thearchives of the Minton factory, founded in 1796 atStoke and also still operating most successfully, is thefollowing, dated 1824:

`Take Gold an Equal quantity an Quicksilver an equal quantityrub them in an Stone Mortar untill you have rub the Silver and

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Heinrich Gottlob KühnA commemorative plaque made at Meissen depicting Kühnas a young man. Trained as a metallurgist, he came to thefactory in 1814, and was a director from 1849 until hisdeath in 1870. After a lengthy series of experiments he wassuccessful in developing a liquid preparation for thegilding of porcelain and although this yielded an extreme-ly thin and not very durable gold coating it none the lessformed the basis of all subsequent preparations

Gold together then divide it in grinders it will take about' /2 anhour to rub a 1/4 of an Oz of Bach this is the Gold most used atthe present time 1824 as Grain Gold as desolved by fire and iswirksome to the eyes and teeth' (6).

The First Liquid Gold PreparationsFor the next major development in gilding techni-

que we have to return to the Meissen factory. In 1814Heinrich Gottlob Kuhn, who had been trained as ametallurgist at the mining academy at Freiburg, wasappointed as technical manager there, the works hav-ing just re-opened after its closure in 1810 during theNapoleonic wars. Economy was essential, and amongother activities Kühn embarked on a long investiga-tion to find a cheaper means of gilding. Not until1827, however, did he finally succeed in evolving anentirely new method, one that laid the foundations ofthe procedures still in use tóday as well as being ofgreat value to Meissen and its future development.

Unlike all other gilding media so far employed,Kühn's preparation was in liquid form and couldreadily be painted on to the ware. It consisted of a

solution of gold chloride in `balsam of sulphur', anoily substance obtained by reacting sulphur withturpentine. This medium — of somewhat uncertainchemical composition — had been known for verymany years and is described, for example, by Neri in'L'Arte Vetraria' of 1612 and by many later writers ofhand-books and encyclopedie. It had been rather ten-tatively employed by Staffordshire potters, includingSpode and Wedgwood, as a basis for a thin lustre byabout 1812, but a full and precise recipe appeared in1824 when the widow of Thomas Lakin, for sometime a partner in Lakin and Poole in Staffordshireand later manager of the Leeds pottery, published abook containing all her husband's recipes, to the greatannoyance of the pottery industry (7). In his Process102, Lakin described the preparation of a gold lustreby mixing a rather dilute solution of gold in aquaregia with balsam of sulphur to give the pink orpurplish colouration normally associated with gold inlow concentration.

A few years later, there appeared in Nürnberg asmall book of recipes for the decoration of pottery andporcelain in which Lakin's procedure was reproduced(8). The authorship is uncertain, but is believed to bethat of one Sebastian Leibl, while the second and im-proved edition, published in 1829, is alone extant andit has been impossible to trace the first edition or itsexact date.

It seems, however, highly likely that Kühn atMeissen was familiar with this work, and that hestarted from Lakin's formula to obtain a truly metallicdeposit by increasing the gold content of the solution.At all events he succeeded for the first time in produc-ing a liquid preparation which, on firing at a relative-ly low temperature, yielded a bright and shining goldthat needed no burnishing or polishing. The goldwas, however, extremely thin and its durability leftmuch to be desired. By about 1.836, nevertheless, thepreparation had been improved, and Kühn couldclaim that Meissen produced the best and mastdurable gold that could - be fired together with theenamel colours (9). This became known as 'Glanzgold'in German, or `liquid bright gold' in English, termsstill used today for the greatly improved modernpreparations.

The secret process, although closely guarded atMeissen, inevitably leaked out, first to Paris wheretwo brothers named Dutertre managed to secure aFrench patent, No. 5336 of 1850, with an additionalspecification in 1861, for virtually the identical pro-cess used in their decorating establishment in the Rued'Angoulême-du-Temple. Their process was submit-.ted for examination by Alphonse-Louis Salvetat, thenchief chemist at Sèvres, by the Société d'Encourage-ment pour I'Industrie Nationale, and received a glow-ing recommendation from this well-informed expert.

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The importante of incorporating base metal additions such as bismuth, cobalt and chromium info liquid gold preparationsto improve adhesion was recognised in the 1850's, but a further vital factor in ensuring the formation of a continuous filmof gold was found to be the presente of a very small percentage of rhodium to reduce surface tension. These electronmicrographs, taken some years ago by Dr. Alfred Boettcher, at that time Director of Research at Degussa, show on the left,at a magnification of 10 000, a liquid gold preparation without rhodium addition fired onto porcelain at 850°C, comparedwitti, on the right, a commercial liquid gold fired at the same temperature and again shown at 10 000 magnifications. Thethickness of application was intentionally varied, but it is elear that the presente of rhodium has had a marked effect inavoiding agglomeration of the gold particles during firing

The Dutertre workshop was then said to be usingsome four kilograms of gold each month and employ-ing five hundred workers (10).

Similarly in Germany, the Meissen gilding methodreached other interested partjes outside the factoryand, by way of two brothers named Schomburg inBerlin, it feil into the hands of a professor ofmathematics and chemistry at Passau namedChristoph Bergeat. A man of restless energy and atireless experimenter in the laboratory in his kitchen,Bergeat, among other investigations, carried out along series of experiments to find an improved formof Glanzgold that could withstand the muffietemperature used for colours. In this he was suc-cessful by 1858 and, after panding over his businessto his eldest son, he died in 1888 leaving a con-siderable fortune (11).

Bergeat was followed by a company in Nürnberg,C. Leuchs and Co., engaged in a variety of activitiesinlading the merchanting of soap and candles andlater the manufacture of perfumes. By 1875 they weresupplying a liquid gold to the porcelain and potteryindustries that was characterised by an exceptionallygood resistance to firing (12).

In England, in 1878, George Matthey provided theMinton porcelain factory with a number of samples ofliquid gold preparations with apparently limited suc-cess, and the lead in this line of business now passedto the Roessler brothers, Hector and Heinrich, and

their company, Die Deutsche Gold- und Silber-Scheide-Anstalt, established in Frankfurt in 1873. Inhis memoirs, Heinrich, the younger brother, recordsthat in 1878 they were offered by one MauricePhilipp, a Roumanian, a process for making liquidgold that had been devised by Dr. G. C. Wittstein, aprivate tutor in chemistry in Munich and a prolificcompiler of chemical and pharmaceutical recipes.Roessler had littie success with this, but his interestwas aroused and he proceeded to have analyses madeof the Passau' gold of Bergeat and the 'Nürnberg'gold from Leuchs. (These identifications remained in.use for many years after the original producers hadceased operations). In Bergeat's product, smallamounts of bismuth, chromium and cobalt weredetected, designed to assist in adhesion of the goldfilm, but nothing of this kind could be found in thesuperior liquid gold from Leuchs. Then, on a visit toJohnson Matthey in London, Heinrich mentionedhis difficulties in competing with the Nürnberg firm,only to be told that they, Johnson Matthey, wererather puzzled by Leuchs' regular purchases of smallquantities of rhodium chloride, at the time a rare andlittie known compound. This gave Roessler the cluehe needed, and by 1879 he was producing a reliableliquid gold fully as good as that from Leuchs.

This was the first entry into the gilding of porcelainand pottery by an established refiner and fabricator,equipped with a comprehensive knowledge of the

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Modern liquid gold preparations can ^V ap-plied to the ware to be decorated by a varietyof mechanical methods, as well as by handpainting. They are therefore produced in arange of forms from thin liquids to thickpastes in order to be suitable for one or otherof these methods, and the measurement andcontrol of their viscosity and otherrheological properties are necessary both inexperimental work and in production. One ofthe instruments used for this purpose is theFerranti-Shirley viscometer in which aspecimen is subjected to controlled shear bet-ween a rotating cone and a stationary plate atconstant temperature. Rheologicalcharacteristics are then calculated from dataon an X-Y recorder, obtained either by pro-gramming the machine to give a plot of stressvs. rate of shear, or by the study of time-dependent effects from the hysteresis loopohtained by an acceleration-deceleration ofthe cone from and to zero

chemistry of gold, and in 1885 satisfactory ar-rangements were made with both Bergeat and Leuchsto take over their products and processes. TheRoessler company, nowadays known of course asDegussa, gathered up all the recipes, solved the pro-blems of stability that had often bedevilled users, andthereafter became the leading producer for a longperiod of years, supplying the products not only fromFrankfurt but from a small plant set up in New Yorkin 1885 (13).

The vital importance of the small content ofrhodium, necessary to reduce the surface tension ofthe gold and to ensure the formation of a continuousfilm, is illustrated in the electron micrographs onpage 125, taken some years ago in the Degussaresearch laboratories.

Modern FormulationsThus commercial production of liquid golds had

begun, and other gold refiners in Germany, Holland,England and France very soon embarked on similaractivities. The liquid bright golds were followed bythe liquid burnish golds, containing a proportion ofgold powder held in suspension and giving a muchthicker deposit but with a matt finish that must beburnished.

The basic compositon of liquid golds was nowestablished, but a great deal of research and develop-ment has of course been carried out over the years byall the interested manufacturers and manyrefinements and improvements have been introducedto meet the needs of individual users. An extensiverange of products is thus available, varying in goldcontent, in colour, in thickness and viscosity, and insuitability for the more exacting requirements impos-ed by mechanical means of application. The produc-tion of finer end more controlled gold powders,together with the use of synthetic resins and otherorganic media, have made possible great advances inthe technology, in ease of firing and in resistance towear of the gold decoration.

Methods of ApplicationTraditional methods of application by hand

brushing remain, while stamping and spraying arealso employed, but for economical quantity produc-tion ingenious machines have been developed toapply both bright and burnish golds to the ware, par-ticularly for banding and lining but also for the directscreen printing of designs. The preparation of liquidgolds for machine application presents certain pro-blems, however, since their viscosity must not change

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Nowadays, the application of liquidbright gold or liquid burnish gold isoften carried out by machines speciallydesigned for this purpose. In thisoperation in the Worcester RoyalPorcelain factory, the liquid gold — arecently developed product fromJohnson Matthey containing syntheticresins and waxes — is fed to the warefrom a heated reservoir and dries im-mediately. The new preparation gives athicker deposit of gold than is obtainedwith cold application and permitsfaster decorating speeds. The machinewas designed and built by F. Malkinand Company of Stoke-on-Trent

too rapidly despite continual exposure to theatmosphere and yet they must dry sufficiently quicklyto enable the decorated ware to be handled in the un-fired state. The speed of evaporation of the volatileconstituents must therefore be carefully controlled inorder to ensure the best possible results under pro-duction conditions.

Where intricate patterns or designs are to be pro-duced in gold the preferred method is to use silkscreen transfers, which give a decoration of higherquality than can be achieved by any other method ofapplication. In this process the pattern is reproducedphotographically on a stencil supported on a fine silkor stainless -steel mesh, and the gold preparation isforced through the stencil on to gummed paper. Alltypes of liquid and burnish golds can be used on silkscreen transfers, together with enamel colours, to pro-duce rich and detailed designs in relief and to yield inone firing well defined patterns that were formerlyunattainable except by skilled hand painting.

The incorporation of certain types of syntheticresins and waxes has recently enabled the user to laydown thicker deposits of gold more quickly, while theintroduction of refractory-stabilised gold powders hasalso been effective in permitting firing at highertemperatures for shorter periods.

AcknowledgementsThe writer has benefited greatly from advice and information

generously provided by the late Dr. Martin Mields, formerlyTechnical Director at Meissen, Dr. Schirer, archivist at Meissen,Madame T. Préaud, archivist at Sèvres, Mrs. Una des Fontaines,Herr Gert Becker and Dr. Max Kollmar of Degussa, Dr. IanFraser, Librarian at the University of Keele, Mr. Hugh Tait of theBritish Museum, and from his tolleagues Mr. F. E. Kerridge, Mr.0. N. Collier and Mr. C. Hood.

References1 Jean Hellot, Registre Y49, in the archives at Sèvres2 J.-J. Bachelier, 'Mémoire Historique de l'origine du régime et

des progrès de la Manufacture Nationale de Porcelaine deFrance', Paris, 1781, 25

3 Alexandre Brongniart, 'Traité des Arts Céramiques', Paris,1844; 2nd edition, 1854, II, 601

4 M. Jean d'Albis, Limoges; private communication5 Wedgwood Archives, Keele University Library, 25: 18073,

18083 and 180896 Mr. Hugh Gibson, Royal Doulton; private communication7 Thomas Lakin, `The Valuable Receipts of the late Mr.

Thomas Lakin', Leeds, 1824, 588 Sebastian Leibl, 'Mittheilungen für Töpferein, Porzellan,

Fayance und Steingutfabriken', Nürnberg, 2nd edition, 1829, 79 Karl Berling, 'Königlich Sachsische Porzellanmanufaktur',

Meissen, 1910, 12810 A. L. Salvetat, Bult. Soe. d'Encouragement pour L'Industrie Na-

tionale, 1861, 8, 12911 Dr. Lingen, City archivist, Passau; private communication12 Dr. G. Hirschmann, City archivist, Nürnberg; private com-

munication13 Heinrich Roessler, 'Geschichte der Arbeitsmethode der Schei-

deanstalt', Frankfurt, 1903, 46

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