Bag of 0.5kg
Calcium carbonate in powder form.
It is used to degrease plates: make a paste by adding water and apply to the plate with a piece of soft cloth or a pad of coton. Rince well. Finally pour a solution of salted white vinegar and rince again. Water should run freely on the surface without repel.
It is also used to improve the whiping of the ink by hand.