One of the unexpected consequences of cutting the cabochon was a bucket of water with a layer of blue sediment (it was used to cool down the grinder while it runs). For many years now, I’ve wondered about creating ultramarine blue from lapis lazuli, but I’ve never gotten around to it. It is a pigment with an amazing history and unsurpassed beauty, so with the powdered rock in front of me, I can’t resist an attempt.
So, to begin with, I simply decantored the collected water and allowed it to evaporate. Once that was finished, I realized that I would need a little more if I was going to attempt the traditional recipe. The Il Libro dell’ Arte by Cennino d’Andrea Cennini that I’ll be following from the early 15th century assumes a pound of lapis powder! If I had an ounce, I figured I could still successfully follow the directions.
My first surprise (I’m sure there will be more …) was that after I prepared an additional batch in my pigment mill it was much bluer in colour. It might not matter in the end, but I went ahead and ground up the full ounce using left-over pieces just to be sure. The lapis was also very hard (it bent the blade of the mill and I had to spend some time straightening it out before I could finish). By pre-crushing the lapis I saved a lot of time and wear in grinding.
The problem with ultramarine blue is that no matter how perfectly blue the mineral sample looks, it has a lot of impurities in it and these grey-out the colour once it is powdered. To remove these, is a difficult job, and reason behind Cennini’s advice. With the powder ready, I need three more ingredients according to Cennini: Pine resin, gum mastic and beeswax. Now where I am going to get pine resin from ..?