Category Archives: Series: Colors

Topazes, Emeralds, and Crystal Rubies. The Faking and Making of Precious Stones

Marjolijn Bol

Today the making and illegal selling of factitious stones has reached an unseen level of sophistication. Advanced technologies allow man to produce synthetic versions of the most precious of stones – diamonds, emeralds, sapphires and rubies (fig. 1). So convincing are these synthetic gems they can only be distinguished from natural precious stones in laboratories with advanced spectroscopic devices.

Fig. 1 Synthetic gemstones
Fig. 1 Synthetic gemstones

The making of imitations of precious stones is not just typical of our modern age. In fact it dates back to at least Egyptian times, as graves from this period show that glass was used to substitute for jewels. Seneca (AD 1 – AD 65) and Pliny the Elder (AD 23- AD 79) were the first authors to write about the practice. Whereas Seneca only mentions that ‘sometimes stones are boiled to resemble emerald (smaragdus)’, Pliny provides us with a rather lengthy account in which he explains the various ways in which gems were imitated. He mentions that glass pastes were used for the imitation of seals and that in some cases stones were cemented together to imitate sardonyx. By a third method, ‘Indian crystals’ were colored with certain dyes to make them look like more expensive minerals. These ‘gems’ were apparently so convincing that ‘(…) there is considerable difficulty in distinguishing genuine stones from false; the more so, as there has been discovered a method of transforming genuine stones of one kind into false stones of another.’ While some physical evidence still survives of the first two practices, the factitious gems made by the third manner, has barely, if at all, come down to us. The many recipes that explain how to make such imitation stones (surviving from the fourth well into the sixteenth century) nevertheless suggest that this last method must have also been practiced, and perhaps even on a large scale. I therefore hoped that a physical reconstruction of the imitation gems might give some further insight into the appearance of these imitation gems. Would it be possible, as the recipes suggest, to make a convincing imitation of a precious stone? Could such a ‘fake’ potentially fool the innocent eye into thinking it was real?

The earliest examples of recipes for imitating stones can be found in the so-called Stockholm Papyrus, a recipe collection written in Greek at about 200-300 AD. The Papyrus includes no less than 71 how-to’s for the imitation of precious stones with lesser materials, including ruby, beryl, amethyst, sunstone and emerald. In subsequent centuries, numerous other recipe books include similar instructions for making counterfeit stones. While the recipes are various, they are almost all based upon two basic operations that I have attempted to reconstruct (fig. 2).

Fig. 2 Opening up of stones
Fig. 2 The opening up of stones

First, a transparent mineral, such as rock crystal, selenite, or topaz, is roughened or ‘opened up’. Following the recipes instructions, I investigated this by cooking the minerals in potash alum (potassium aluminium sulphate) dissolved in vinegar. As soon as I removed the heat from this mixture, it rapidly crystalized into a hard crust around the stones. In accordance with the recipes I left the stones overnight.  Nevertheless, when I inspected them the next day (after having chiseled them out) I could not see any changes. Regardless of whether the stones were successfully ‘opened up’, the coloring of the minerals did produce some surprising results.

The recipes instruct that the ‘opened up’ mineral should be colored using a mixture of a colorant ground with oil or resin to make it assume the appearance of a specific gemstone. The dyes and pigments used varied according to the type of gemstone that was to be imitated. A red dye made from alkanet root (used by ancient cloth dyers) was advised for the imitation of rubies and the green copper pigment verdigris was used to transform transparent minerals into emeralds. For my first reconstructions I choose to make a ‘fake’ emerald. It was one of the precious stones imitated the most frequently and the instructions for making it remained almost the same through (post-) classical and pre-modern times (fig. 3).

Fig. 3 Coloring of stones
Fig. 3 The coloring of stones

I first ground the pigment verdigris with linseed oil and used this substance to cover the base of a rock crystal, topaz and piece of selenite. This resulted in a beautiful, translucent green stone that, due to the instability of the pigment verdigris, in time assumed the saturated forest green color of a real emerald. Whereas more reconstructions are certainly required to investigate the nature of this method of gemstone imitation, these first experiments show that, when ancient sources insist how visually convincing the imitations of precious stones could be, they are probably not exaggerating.

Fig. 4 Emerald imitation
Fig. 4 Emerald imitation

Recommended reading:

Marjolijn Bol, ‘Coloring Topazes, Crystals and Moonstones: The making and meaning of factitious gems, 300-1500’, in Marco Beretta and Maria Conforti (eds.), F for Fakes: Hoaxes, Counterfeits and Deception in Early Modern Science, 2nd Watson Seminar in the History of Material and Visual Science, Museo Galileo, Florence, June 7, 2013, Science History Publications (Brill Publishers: 2014), pp. 108-129.

Earle R. Caley, “The Stockholm Papyrus: An English Translation with Brief Notes”, Journal of Chemical Education 4 (1927), pp. 979-1002.

Pliny, The Natural History, books 33-37 (book 36 includes Pliny’s natural history of stones):

The (lack of) power of gemstones

By Marieke Hendriksen

The idea of gemstones having curative powers has existed from ancient times until the present day. As I am interested in the use of chemical and mineral substances in eighteenth-century Dutch and particularly Boerhavian medicine, I am currently analysing medical and apothecary handbooks from this period and area to gain an idea of what eighteenth-century Dutch physicians and apothecaries thought of the alleged curative powers of gemstones. Unlike neighbouring countries, the Netherlands has no strong tradition of early modern lapidaries, so I was somewhat surprised to find regular mentions of gemstones in these sources anyway.

Front page of the 1741 Leiden edition of the Medicina Pharmaceutica
Front page of the 1741 Leiden edition of the Medicina Pharmaceutica

A number of examples can be found in a 1741 Dutch apothecary handbook about which I have written before here. It was re-edited by an apothecary, Schróder, and initiated by Boerhaave’s direct successor as professor of chemistry at Leiden University, Jerome Gaub: Medicina pharmaceutica, of Groote algemeene schatkamer der drôgbereidende geneeskonst, originally published by the Flemish apothecary and physician Robertus de Favarques. The new edition of this 1681 work appeared with the Leiden printer Severinus, and was received positively in the press. In De Favarques’/Schróder’s list of simples, an entire section is devoted to metals, minerals, and stones. Not only were the materials listed, but also an overview was given of where they were found and how they could be used in the apothecary shop. From these descriptions, it becomes clear that the powers of some metals and gemstones were still commonly accepted, whereas those of others seem to have fallen into disrepute.

Natural ultramarine pigment, made of powdered lapis lazily. Works a treat if you're feeling blue...
Natural ultramarine pigment, made of powdered lapis lazuli. Works a treat if you’re feeling blue…

Pulverised rock crystal for example is mentioned as a cure for diarrhoea, powdered lapis lazuli is prescribed to strengthen the heart and to alleviate melancholy. However, the authors are more sceptical about the uses of some other stones, especially when worn on the body. The eagle stone – not a true gemstone but some sort of hollow clay stone, is commonly believed to prevent miscarriage when worn around the neck, to ease labour when tied around the calf, and recommended by some in plasters to treat convulsions. However, the handbook warns, they are only good to stop bleeding and diarrhoea when taken in powdered form. Garnet and ruby, although commonly attributed with cordial powers, as well as with the power to ward off melancholy and venom, in this book too serve only in powdered form to curb sharpness in the body, to temper the flow of blood and faeces, and to dry. Similarly, it is said of sapphires that many powers are ascribed to them, which they do not possess, such as cordial, blood cleansing, and other powers. Basically, apart from lapis lazuli, all stones and gemstones in the list only qualify in powdered form as absorbents to stop bleeding and diarrhoea; no other applications are mentioned.

This focus on (gem)stones as only useful in medicine in powdered form to stop all kinds of bodily fluids from flowing freely suggests a strong humoural understanding of the medicinal powers of stones, the dry earthiness of which could temper the wetness of blood and phlegm. Moreover, the list shows a rejection of early modern understandings of (gem)stones as having curative powers from which one could benefit by wearing the stone on the body. Exactly why he seems to have thought lapis lazuli -the only source of expensive ultramarine pigment until the early nineteenth century- was an exception remains a mystery for now, but maybe I will be able to inform you about that in the near future…

Illuminating the ‘elusive’: reconstructing mediaeval recipes for anthocyanin pigments

By Sylvie Neven

Due to their trade value, a huge range of artistic materials is documented and recorded in historical written sources, such as guild regulations, contracts between artists and patrons or pharmacy price lists. However, certain substances are not recorded in these types of archives because they did not have market value. This is notably the case for plant-based materials that artists could easily find in nature and use for their colouring properties, such as the anthocyanin colourants. As these colourants are highly unstable in ordinary daylight, it was generally thought that they were not used in the dyeing of quality materials or to make paint but rather employed in a domestic context, as dyes for everyday clothes. To complicate the issue, anthocyanin colourants are difficult to identify through currently available analytical methods. For all these reasons, these substances have long remained ‘elusive’.

Nevertheless, research on mediaeval artists’ recipe collections has highlighted that a number of these books not only describe these organic colourants, but also indicate their use in illumination[2]. Based on a corpus of more than 400 mediaeval artists’ recipe books, this project intends to analyse the significance of these organic substances and to (re)define their use in an artistic context. In order to find citations of anthocyanin colourants throughout a vast amount of recipes, a specific database of artistic recipes was used (‘Colour ConText Database’). This database enables easy identification of recipes dedicated to anthocyanin colourants and allows researchers to deduce the availability of these colourants in a chronologically and geographically defined area. The database also makes it possible to establish and compare the different ways in which these colourants were prepared.

Thanks to this tool, I have found that the use of anthocyanin colourants is particularly frequent in the artists’ recipe books of the so-called ‘Strasbourg tradition’. Within this group, the recipes describe the use of corn poppies (Papaver rhoeas L.), blue cornflowers (Centaurea cyanus L.) bilberries (Vaccinium myrtillus L.), and elderberries (Sambucus sp.) for producing colours.

sylvie flowers 1
Papaver Rhoeas L. & Centaurea Cyanus L.
sylvie flowers 2
Vaccinium myrtillus L.
sylvie flowers 3
Sambucus sp.

From these sources, it becomes clear that anthocyanin colourants were used for modelling and shading in the realization of flesh tints, draperies and landscapes. Furthermore, they also appear to have been applied as glazes on layers of gold or silver and served for making the inks that were used to underline rubrics or elements of decoration in illuminated manuscripts.

The basic operation is relatively simple and similar from one recipe to another. The petals or the berries are ground and crushed in a mortar in order to produce a foam. The juice is then extracted by filtering the foam through a clean (linen) cloth.sylvie pestle

sylvie foam

sylvie juice

The recipes mention several sorts of additional ingredients. For example, alum (potash alum or aluminium sulphate) is mentioned frequently and could have various functions. Its addition can modify the pH and provide aluminium cations that have an impact on the final hue and improve the stability of the colorant.

In order to be used in painting and illuminating, anthocyanin colorants were preserved by setting them on a small piece of cloth, mentioned in the recipes as tüchlein or pezette, usually known in English as a ‘clothlet’. These pieces of cloth were first steeped in the prepared juice until they were saturated by the dye solution. After drying, the pieces of cloth were then wrapped in clean paper and kept between the pages of a book or in a wooden box, and stored in an area free of humidity. To use a stored colorant, the artist would cut off a small piece of the dyed cloth, place it in a shell or horn and pour some gum water or other sort of binding medium, such as egg white, onto it.

With the help of Dr Sanyova (KIK-IRPA), I have reconstructed a number of recipes of the so-called ‘Strasbourg tradition’ in the laboratory. Our purpose was to establish the different ways in which these colourants were prepared and explore how they were used in illumination techniques. We focused on comparing different procedures to make colourants from anthocyanins. The possibility of collating different manuscripts of the same textual tradition allowed us to study the evolution of recipes for the preparation of anthocyanin colourants both through time and through different copies. The numerous recipes recommended the use of different plant species and ingredients in varying quantities.

Dummy samples before and after artificial ageing process
Dummy samples before and after artificial ageing process

Over the period of several weeks, we prepared series of dummy samples of red and violet tüchlein from the juice of petals of Papaver rhoeas L. After that, the samples were evaluated by visible spectrophotometry and high performance liquid chromatography (HPLC), before and after the artificial ageing process. We found that the different recipes created a number of saturated hues providing artists with various colours.  However, interestingly, the products of the different recipes all responded similarly to the artificial ageing process.

[1] Anthocyanins are colourants that provide most of the blue, red and violet colours in numerous plants and fruits.

[2] Notably : Neven, S., ‘The Strasbourg Family Texts: Originality and Survival. A Survey of Illuminating techniques in Medieval South Germany’, in Revista de Historia da Arte, n° especial, 2011, pp. 65-77; Neven, S., ‘Describing the “elusive”: a new perception of the practices and the resources of illuminators in the North of Europe from the fourteenth to the sixteenth century, in Renaissance Workshop, London, pp. 188-190.

Prescribing and Describing Art Technology

By Marjolijn Bol

“To Produce a Gold Color by Cold Dyeing.

Take saflower blossom end oreye, crush them together and lay them in water. Put the wool in and sprinkle with water. Lift the wool out, expose it to the air, and use it.”

Stockholm Papyrus (Old-Greek, 4th Century AD)

This recipe describing how to dye wool a golden color is just one example of the many sources on art technology that have come down to us as from as early as 2000 BCE. The recipes range from the making and working of parchment, stone, glass, textiles, paper, pigments and colorants – to the production of embroidery, miniatures in books, metalwork, enamels, ceramics, woodworking, panel painting, glass painting and much more. Here on The Recipes Project, readers have already encountered several posts dealing with topics on art technological sources (see hereherehere and hereand more are planned for the future. For this reason the idea came about to develop a series of posts highlighting the current scholarly initiatives and interest into artists’ recipes.

An art technological source can be understood as any material surviving from the past that provides us with information about the history of the materials, tools and techniques used to make works of art – ranging from realia, to the work of art itself, images, texts and audio-visual sources. In the present series of posts, however, we will focus mainly on art technological sources in the form of recipes – or written records of artistic production. Interestingly, research into art technological sources has also triggered the field of historical reconstructions. On the basis of artists’ recipes, scholars attempt to reconstruct certain painting techniques, metalworking methods, lost objects from material culture such as parchment windows or factitious gemstones and much more. These historical reconstructions help scholars better understand the recipe, re-materialize long-lost objects that we now only know through textual sources and provide insight into the ‘original’ appearance of objects that survived in poor or changed condition. As a result, historical reconstructions can offer us a glimpse into the complex processes through which a certain artwork was made.

In recent years, the study of these so-called art technological sources has gained much momentum within the fields of Art History, Conservation & Restoration and the History of Science. In 2002, the Art Technological Source Research Group (ATSR) was established within the International Counsel of Museums (ICOM-CC) providing research into art technological sources with an international scholarly platform. Whereas many more recent initiatives could be sketched out here, I will only mention two more in the context of the present blog series. In attempt to organize and systematize the vast amount of historical artists’ recipes, the Max Planck Institute for the History of Science in Berlin is making a vast database on historical recipes on art technology (‘Colour ConText‘). Furthermore, the importance of research into art technological sources is attested by the fact that, since 2012, the University of Amsterdam has offered  a masters course on the topic. This course in Art Technological Source Research is not only unique because it brings together students from the Conservation & Restoration and Art History courses, but, additionally, the students have the opportunity to study original recipe books collected by and kept in the library of the Rijksmuseum. All students study a particular recipe from a treatise in the Rijksmuseum collection and make a historical reconstruction of the said recipe as part of their studies. We had groups of students attempting to grind and process petuntse stone according to an 18th century recipe for making Chinese Porcelain, while another group attempted to find out the role of spike oil in an 18th century varnish recipe. The students from textile conservation reconstructed the color “violet” from Runge’s Farbenchemie (1842) and, finally, the fourth group of students made a reconstruction of a painted silver vessel according to a recipe from Wilhelmus Beurs’s The Big World Painted Small (De groote waereld in t kleen geschildert, 1692).


The posts in this series titled Describing and Prescribing Art Technology intend to form a first glance into present-day research into art technological sources. It highlights the special collection of recipe books at the Rijksmuseum of Amsterdam with an interview with the head librarian Geert-Jan Koot. Later in the month, Ad Stijnman, a key member of the Art Technological Source Research Group, will tell us a little about the history and research scope of this group, and, finally, Sylvie Neven will offer us a fascinating example of research into artist’s recipe books.