32 - Emerald Green Glass
In making green take into consideration that the glass should not have a lot of salt in it.
If you use glass that does have a lot of salt, like bollito and rocchetta, you cannot make a beautiful green but only aquamarine, since the salt consumes the green and it always inclines to a bluish marine colour.
Therefore, when you want to make a beautiful green, in a large or small crucible put common glass made with polverino, as can be seen in chapter 8. Use glass that has never, in any manner, been shown manganese, because then your work would appear dark and ugly. Once it is fused and very well clarified, add a little crocus of iron to this glass, which has been calcined with vinegar, as is described in chapter 17. So as an example, for 100 pounds of glass add approximately 3 ounces [of crocus]. Leave the glass for an hour, then stir well until it incorporates the crocus pigment, which makes the glass become somewhat yellowish and removes the scum and bluishness that glass always has. This work will give the glass a beautiful green tint at which point add the 'thrice baked' copper made of scale from the hammerings of kettle smiths, as shown in chapter 28. For this the rule is to use 2 pounds for every 100 pounds of glass, added in six portions. Mix the powders well with the glass, and then leave it for 2 hours to settle down and incorporate into the glass.
At this point return to mix the glass and see if your colour is sufficient, and in compliance for its intended use. You may need to add more copper scale to produce the colour, and you may need to charge it more or less according to the work and use. If you need to make some adjustments, I cannot give you precise rules. lf the green inclines to the marine and bluish and it does not appeal to you, add a little bit more crocus of iron, as above, to obtain a most beautiful emerald green also known as leek green. At the end of 24 hours it will be ready to work. Be ever vigilant; before the glass is worked make sure to stir it, because the colors always go to the bottom and on top the crucible is often more [colour] free. I made this green
in Pisa and it always came out quite beautifully and with such success every time, as it will for you; just follow the instructions step by step, as I keep saying.