A friend linked to a short online collection of pictures of alchemical manuscripts, which included a 15th century Germany/ Austrian Donum Dei of pseudo-Arnaldian type, or at least it refers to him a few times.
Now the interesting thing is the vessel, which is unlike any I have seen elsewhere. It is like an upside down alembic, but sealed except for the spout. How precisely it is supposed to work is unclear. So that is the first mystery, although it might be based more on my lack of knowledge of alchemical vessels, and of course the lack of any real broad study of them despite their widespread existence throughout many hundreds of surviving manuscripts.
The second interesting point is the colours used in the pictures. There is of course a red king inside it, a white queen, as usual for 15th century alchemy, and one picture has this:
Which is the same odd sort of flask with lower half labelled aqua, the captions saying something to do with philosophical sulphur and whitening and cleaning the black and white.
But note the three red circles, three white, two green and two blue. Is this an accident that they are probably the four elements, red being fire, blue perhaps air, or what? Colours turn up frequently within alchemical illustrations and descriptions, but the only ones people have really noticed are the red and white. Of course the four elements correspond to specific colours too, but not always the same ones. Which is where it gets tricky, because previous research I have done couldn’t reach a decent conclusion about the use of colours within one alchemical manuscript, and if they had a definite purpose and meaning to them in the specific situation. In general, alchemists seemed to have different ideas of what each colour meant, or when it was supposed to appear in the alchemical work. Red, white and black are important, but not generally blue, which is associated more with one of the elements, air or water.
So if I were being adventurous, I would suggest that it means you need equal amounts of red and white and lesser of green and blue, and they might correspond to the four elements. But that is just speculation at this stage and it is more likely that they don’t mean anything. More research required as usual.