Carries the Palm Reprise

Entry into Jerusalem, Pietro Lorenzetti 1320

For Western Christians, yesterday was "Palm Sunday," a feast day that falls on the Sunday before Easter and celebrates Jesus' entry into Jerusalem. His procession is said to have included his followers laying palm tree leaves before him along his path. The connection to seventeenth century priest and glassmaker Antonio Neri is this: In his book L'Arte Vetraria, Neri describes his very best green glass with a colloquial expression; that this recipe "carries the the palm" for all other greens. It seems like an ideal opportunity to reprise this post, which first appeared last year, on 25 October:  

Saint Justina of Padua with a palm frond,
Bartolo Montagna 1490s

In his book, L'Arte Vetraria, Antonio Neri presents a string of recipes for variations of green glass. Finally, in chapter 35, he presents his ultimate green, which he titles: "Another Green, Which 'Carries the Palm' for All Other Greens, Invented by Me." The phrase "carries the palm" alludes to the biblical story of Jesus entering Jerusalem, in which the people welcomed him by laying down cloth and palm branches on the ground in his path. Even before that, the palm branch served as a symbol of victory; in ancient Greece, palm fronds were awarded to victorious athletes. Later in history, Roman lawyers who won a case decorated their doors with palm leaves.

Copper Sulfate (vitriol of copper)

Cristallino was a mid-grade glass made with a soda based plant ash from the Levant called "rocchetta." For this recipe, Neri blends it with common glass, and adds red lead oxide to the mix, in effect forming an early version of what we now call lead crystal. He "cleans" the glass by using the well-established technique of flinging the molten glass into a large tub of clean water. This had the effect of "washing out" excess glass salt (flux). In addition, it provided the opportunity to sort through the fragments to remove any undissolved metallic lead. Lead that did not go into the glass had the tendency to collect at the bottom of the clay crucible. It could then eat a hole in the vessel, resulting in a glass-shop disaster, as he warns: 

All lead precipitating out of the glass must be removed with diligence, throwing it away, so that it does not make the bottom of the crucible break out, as can happen. Return the glass that was thrown in water to the crucible and leave it to clarify for a day. Then add the color using the powder, made chemically by the dry distillation of vitriol of copper [chapter 31]. Also, add a little crocus of iron, but very little. The result will be a most marvelous beautiful green, the best that I ever made. It will seem just like an emerald of ancient oriental rock, and you can use it in every sort of job.

Crocus of iron is simply iron oxide or 'rust' as it is more commonly known. The vitriol of copper he refers to is copper sulfate. Neri forms it in a laborious process that involves cutting copper sheet into small, coin-sized pieces, mixing it with sulfur, heating in the furnace and then reprocessing it several times. The result is then added to water and the soluble part is further processed, filtered and evaporated. The final product is a pure blue crystalline material that has uses for our alchemist that go far beyond glassmaking, as he alludes to in the final sentence of the book:

Although I have placed here the way to make this powder with much clarity, do not presuppose that I have described a way to make something ordinary, but rather a true treasure of nature, and this for the delight of kind and curious spirits.