Pumice stone, a volcanic substance, is a porous silicate of alumina and alkaline earth mineral. Asbestos is a fibrous silicate of magnesia and calcium, and this is why that extender, known as asbestine, that has during the last ten years come to the forefront in paint making, which is really a silicate of magnesia and slightly alkaline, but without the fibrous texture of asbestos or amianth has been given that name. Asbestine pulp, as a certain variety of the material mined at the foot of the Adirondack Mountains is known to the trade, although it is sold in the dry powdered form, belongs really to the soapstone or talc variety. But it is not as unctuous as either of those, has a harder texture, and is of whiter color than either soapstone or talc. Soap-stone or talc is used for toilet powder and as a lubricant by shoemakers, also on dancing floors, in fillers, putties and cements, but not as a rule in paints. Asbestine pulp or asbestine in its various varieties has been used for many years by manufacturers of liquid paints, not so much as an adulterant, but rather to make the paint more buoyant in order to keep it from settling to any extent, as this pigment is of very low specific gravity and a great oil absorber. This feature, however, depends on the location where it is mined, as there is a wide divergence in that respect. Its specific gravity varies between 2.3 and 2.7 and its oil absorption is between 30 and 36 per cent, or in other words, to make a paste in oil will require 70 pounds of the heavier asbestine to 30 pounds of oil or 64 of the lighter asbestine pulp to 36 pounds of oil. If manipulated in a chaser a stiff paste could be produced in either case with 10 to 15 per cent less of oil.
Asbestine is used to some extent in making liquid fillers for soft wood, and with the proper kind of varnish the material holds far better in suspension than China clay, and certainly much better than silex or silica. Mixed with silicate of soda (water glass) it makes a very good fireproof coating. Asbestine is as inert as barytes or silica, and does not undergo a chemical combination with oil or water, but will be found sometimes more or less alkaline, and while it may be safely used as an extender with most any color, it has been found to be active on Prussian or Chinese blue when used in large percentages in admixture.