Renaissance paint
It's only been in recent times that artists (and children) have bought paint in shops and even today some artists still make paint the old way.
How do they do it? The specific ingredients depend on the sort of paint you want to make, but the basic principles are the same for any paint: you need the colour and something to make it into a paste or liquid (this is called the medium).
Many colours start off as earth or stones. Reds and browns are often earth colours. Some blues are made from ground-up blue glass. Another blue is made from the semi-precious stone, lapis lazuli. This makes the blue colour called ultramarine, which was more expensive than gold in the Renaissance period.
The medium usually consists of something sticky which can then be diluted to make the paint workable. Lots of different sticky substances were used, including egg, different oils, beeswax, and even earwax! The diluents (liquids to dilute the paint paste) could be more oil, varnish, water, leaf sap, and even urine! So, there are two reasons why you should never touch the surface of a work of art: you might damage it, and it might damage you!
A little bit of Alchemy
The alchemists used special names for many of the chemicals we know today. Many of the names were poetical, or described how the chemical looked or was used. Mercury, for example was called quicksilver because it's a silver liquid that slithers away from you very quickly. In the excerpt from the Secretissimus Secretorum the masked nobleman talks about aqua regia and Jacopo mentions vitriol. These are both acids.
Vitriol is sulphuric acid. You may be familiar with this from school. In its concentrated form it will eat through your skin. Even diluted it will leave holes in your clothes if they get splashed.
Aqua regia is an even scarier liquid. It is a mixture of two other acids (hydrochloric and nitric), but what makes it dangerous is the chemical reaction that takes place when you put these two acids together. If you know anything about how modern chemical names are put together, you might be able to guess what will happen. The 'chloric' bit of the first acid refers to chlorine, and nitric bit of the second acid refers to nitrogen. When you put these two together chlorine gas is released, along with a few other things. Chlorine gas is the stuff they put into swimming pools and drinking water to clean it. It's fine in small amounts. But in large amounts it kills. That's why the nobleman was so keen to get away from it.
