This week a reader asked me this question- is there lead in smalti? Smalti is the glass used for making Italian style mosaics such as the many ancient mosaics to be found in the wonderful city of Ravenna in Italy.
There are a number of elements that make up the special smalti glass. In the early days the composition of basic colours included compounds such as washed sand, saltwort powder, ground crystal, antimony, lead lime, minium (red lead), lead and tin lime, lithagrge, iron oxide, copper filings, salt, green chromium oxide, smalt, glass cotticcio, iron flakes, arsenie, crystal and pure gold.
So yes there is lead in today’s smalti too. This a topic that is not often discussed but should be given serious consideration when working with smalti. Here is an excerpt from Glass and Ceramics, , Volume 25, Issue 4, pp 225–227|Producing smalti for mosaics by N. P. Danilovaand K. A. Bryukhova- in the Academy of Art of the USSR, Leningrad. Translated from Steklo i Keramika, No.4, pp. 20-22, April, 1968.
“In recent years the stocks of many of the colors of the old Smalti have been exhausted or have dwindled. To supplement the scarce colors it has been necessary to develop new basic smalti compositions, to select colorants, and to perfect production techniques.
It is impossible to accurately reproduce the chemical composition of old smalti from existing literature data and recipes contained in the science bibliographical archives of the Academy of Sciences of the USSR, since almost all of these recipes involve the use of culler glass from various factories, and instead of pigments, colored fusions and alloys of unknown composition are used. Furthermore, we have no precise analysis of the raw materials that were used. However it is known that all smalti was made on a lead base
which ensured a high density and excellent cleavability; according to approximate data the smalti compositions contained 15-56% lead oxide. The opacifying agents consisted of Sb203 in amounts of 10-12%, SnO 2 in amounts of 15-20%, and 8-10% As203, that is toxic, scarce, and expensive materials. The melting and heat process cycles for smalti are not given in any source,. In 1940 the glass department of the Leningrad Institute of Technology developed new smalti compositions, using fluorides as opacifiers (6% fluorine). A total of 120 smalti specimens of various colors and shades was developed, using the conventional technique“.
In another book, the Annales Du 17e Congres D’Associationo Internationals Pour L’histoire Du Verre 2006 Antwerp, Don Christoforo describes the materials used to make smalti. ‘Physica is the raw glass that works best for producing smalti. In a process similar to processes used in enice, the glassmaker takes ten pounds of physica and adds one pound of lead…. The result is a lead glass that is ready for colouring and marketing as smalto. The best smalti he adds, are made by including ashes of tartar (an alkaline deposit on the inside of wine barrels) in the melt.‘
Smalti recipes are jealously guarded by the manufacturers of these tiles; this has always been the case with smalti production, because of the fierce competition amongst mosaic artists. As a result it is hard to discover just what the product contains.
But have no fear – there’s is eco smalti which is made of ground marbles, granite and precious stone. I have not used the product myself yet. Here’s the link to the website. Certainly the images would suggest that the product does not have the wonderful vibrance of lead smalti. But perhaps health should be the primary consideration. http://www.xinamarie.com/mosaic/smalti-chunks-c-1_54.html
So when working with smalti take sensible precautions – work in a well ventalated room, if you’re working extensively with smalti cover your mouth….