Nature transmuted into silver

Looking into the presence of turtles in artworks has turned into a little bit of an obsession for the Turtle Team. Every storyline has provided new ideas and insights into the context of the object this all started with: The Portrait of Prince Frederick Henry on Horseback (1631), painted on a large green sea turtle carapace. It is absolutely fascinating how turtle scutes were one of the many biological materials used by 16th and 17th-century artisans in beautiful artefacts,  for the Kunst Kammer or Cabinet of Curiosities. But turtles were also cast in metal, often by anonymous artisans and sometimes by famous gold and silversmiths.

Nature transmuted into silver

The water turtle is more beautiful to mold because it has prettier scales & straight legs. And those of the garrigue have crooked ones. They are of long life; getting ready to put them to death, open their mouth & pass a long penknife through all the intestines, & then make it swallow some vinegar mixed with eau-de-vie or urine, as for snakes…

This quote from a late 16th-century French manuscript kept at the Bibliothèque national de France, in Paris (BnF Ms. Fr. 640, folio 143r)*, describes the rather gruesome preparation of turtles for molding and casting them in metal. The garrigue indicates shrubland terrain characteristic for southern Mediterranean coastal areas and home of, for example, the now endangered Testudo hermanni with its characteristic black and yellow carapace. Water turtles in France and elsewhere in Europe concern mostly the so-called European Pond Turtle or Emys orbicularis. Both species are small and their baby turtles seem quite similar to the tiny turtles that can be found, together with small lizards and plants, on the foot of a rather magnificent table piece from 1549 (99.8 x 46 cm, silver, email) , by the Nuremberger goldsmith Wenzel Jamnitzer (1508-85) in the collection of the Rijksmuseum.


Jamnitzer was a master in casting from life, where the animals, insects or reptiles, were still living when they were put in molding material and then burnt out in the kiln. Hot liquid silver or other metal was poured in the mold, filling the space left by the animal. The mold had to be broken to free the cast sculpture; the so-called lost pattern method, but there were other methods used where the pattern was saved. Were Jamnitzer’s small turtles cast from life, just like the little lizards?

Life-casting was extremely popular across 16th-century Europe, especially the casting of rare or unusual natural materials as well as real but perishable objects. Artists thus imitated nature’s transformative powers through the transmutation of hot fluid metals into natural forms such as lizards and plants. The choice for lizards, snakes, frogs, turtles and insects in particular, connects to the fascination with the transformative character of these creatures, who would shed their skins, regrow tails, come back to life after hibernation, and transmute from caterpillar to butterfly. 17th-century natural philosophy considered the imitation of nature through artisanal processes as equal to understanding nature: making is knowing. For the artisan this entailed a thorough knowledge of the properties of the materials and processes used. Life-casting was practiced well into the 17th century and many museum collections hold objects representing this practice.

BK-2009-79 (1)
Snake, Lizard, frog and mouse, anonymous, Italian, c. 1550 – c. 1599
‘life cast’, in double mold, 23.7 cm × 15.8 cm, Rijksmuseum, Amsterdam (BK-2009-79)

For example, the Rijksmuseum owns this rather curious group of a lizard, snake, mouse and frog entwined, seemingly lifecast. Again, Bnf. Ms. Fr. 640, provides direction, not only for each individual creature, but also on casting ‘various animals entwined’. These instructions could in fact have been used for this piece, where only the poor mouse, strangled by the snake, is added to the composition:

You can entwine a snake with a lizard, one biting the other, or a snake that eats a frog or a wall lizard & suchlike. But because these entwinings can in no way make a good release, cut what you can & leave the rest to burn. And to keep a wall lizard, which is small, in the mouth of the snake, which is raised & needs to be supported in the air,  because the head of the snake is posed raised, put underneath the wall lizard an elevation of earth suited to support it. And if you put your mold in the oven, the animal, drying promptly, will retract & will burn better afterward.  These entwinings are also made to cover a wound or fault in the animals, which one usually wounds when one catches them… For further instructions read folio 133v here

The molding of turtles is also comprehensively addressed in the French manuscript. The author-practitioner seems to have executed many of the recipes himself, as the text very much resembles working notes, which indicate ample experimentation to build a thorough understanding of the nature of the materials and processes used. We know that the lizards in Jamnitzer’s table piece are cast after life following a method as described in BnF Ms. Fr. 640 [folio 111r]

Although, as the recipe explained, the turtles are not directly cast after life, they were only dead for a few days, to make the modelling of the turtle easier as its legs and head would relax. There is a lot of attention for detail as the author practitioner suggests lifting the head by supporting it with some fresh clay and to stretch the head and legs with little pincers. He advices to replace the eyes which ‘burst and get putrid’ once the turtle is dead, with grains of yellow millet, amaranth or rapeseed. The turtle can be supported with small metal pins. Small drawings in the margin illustrate the positioning of the turtle as well as the beady eyes.

Instructions are given both for a lost-pattern method, as well as for a method that preserves the turtle without burning it. The latter is complicated. Especially taking the mold  apart to release the model, requires a lot of skill:

Usually one begins with the back shell, that is to say, the mold on top, which is in two halves, and this one is easier to release. The other one follows after, but because it is neighboring the shoulder of the turtles, which are deeply ensconced, it is sometimes awkward. Thus, when moving & pulling the mold gently, take heed to pull the one which will present itself as the easiest, for one needs to release one after the other. The most awkward of all is the one which molds the throat, the underneaths of the legs & the hollow shoulder pieces, which are of such bad release that if you had not provided for it, by filling with wax before molding what does not release well, it will be awkward for you to pull your pieces out without breaking something [folio 147r].

The various extensive and elaborate molding processes are described on folios 143r-144r, and 146v-148v, 1550v-151v , which you can read here. As the author-practitioner states: ‘There is more work in molding a turtle than for twelve molds of flowers’ [folio 151v].


Tortoise, bronze, Padua?, early 16th C.
Museum Boijmans van Beuningen,
Rotterdam, 7 x 18 x 15,5 cm, 1117
The same tortoise upside down, showing it was hollow cast after life using a core (see Molding Hollow reconstruction and recipe)

Baby turtles: real?

Returning to the small turtles in Jamnitzer’s table piece: the use of real turtles has been doubted, as the lines in the pattern on the carapace are considered to be too deep. It has been suggested that a wooden model was used. However, in BnF. Ms. Fr. 640, advice is given on how to work the surface after casting:

To repair, if the features are not apparent enough, retrace them lightly with a burin, then soften them with a small chisel. The flashing is removed with the chaple, a type of burin. For the lumps & scales, they are made either with a little gouge or a little round cutting-punch, or with the point of a small chisel, not tempered, & struck on a small file [folio 148v].



Mercurius gives instructions to a silvermsith, anonymous, 1600 – 1700
etching and engraving, h 182mm × b 122mm, Rijksmuseum (RP-P-1887-A-11501). See the many tools displayed on the wall behind, plus kiln, scales and other materials. 

First of all, the flashing, the excess material, caused by leakage of the metal between the various parts of the mold, needed to be removed. Next, specific tools are listed to retrace features, and to work on the lumps and the scales of the turtle.

With these instructions in mind, and comparing a real baby turtle with the one in Jamnitzer’s table piece, it is not implausible -although more research would be needed- that the small turtles could have been cast after real ones, with the lines in the surface of the carapace and the scales on the legs and head reinforced and stylised as the instructions suggest. Jamnitzer added colour too, which brings the small turtle even closer to its natural counterpart. Nature transmuted into silver.


The Turtle Team


Molding a turtle hollow

One can also mold hollow instead of solid, to prevent the cast turtle to be too weighty, a method that was reconstructed by Tonny Beentjes, head of metal conservation at the University of Amsterdam, who followed the instructions by hollow casting a crab as turtles are fortunately not easily available.  Here is the reconstruction based on the recipe in BnF. Ms.Fr. 640, folio 150v and ff. for Molding a turtle hollow.





* BnF Ms. Fr. 640, folio has been the focus of a multidisciplinary research project Making and Knowing, at the University of Columbia, New York City,  led by Prof. Pamela H. Smith and a large team of researchers and practitioners. A full edition of the text, which most resembles a so-called Book of Secrets, due to the great variety of recipes from artisanal to the medicinal, representing ‘intersections of craft making and scientific knowing’, including the facsimile and English translation is available online. Do explore as there are many fantastic and insightful essays, reconstructions etc. accompanying this fantastic source on Renaissance artisanal knowledge and techniques.

The Making and Knowing Project, Pamela H. Smith, Naomi Rosenkranz, Tianna Helena Uchacz, Tillmann Taape, Clément Godbarge, Sophie Pitman, Jenny Boulboullé, Joel Klein, Donna Bilak, Marc Smith, and Terry Catapano, eds., Secrets of Craft and Nature in Renaissance France. A Digital Critical Edition and English Translation of BnF Ms. Fr. 640 (New York: The Making and Knowing Project, 2020),

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