The 19th century description of ‘grinding malachite’ to reduce it to powder for pigment is completely erroneous, and effective processing requires smashing or crushing – most likely with a hammer stone against an substantial anvil stone as shown in Figure 1 and also in video demonstration here: http://www.instagram.com/p/BksM2HQgT-s/
This percussive smashing and crushing produces small crystal shards which are extremely flyable. To contain these, the malachite would be wrapped in a material such as leather or linen. This material would most likely be scrap from clothing or other use, as it is destroyed during the crushing process. This destruction of the wrapping material imparts microfibres, with diameters ranging from 8μm to 23μm, into the resultant powdered malachite as can be seen in Figure 2.
The powdered malachite would be mixed with a base before use, such as a lipid base for use in ‘cosmetics’. The presence of the microfibres may help to reinforce the resulting pigment, thus helping to reduce shrinkage and cracking in a manner analogous to the reinforcement of mudbricks with straw
This microfibre reinforcement may be a part of why green pigmentation appears to survive extremely well on the surface of palettes in the Predynastic era and also in the later Dynastic era (as can be seen in Figure 3).