It seems that when this subject surfaces, a few suggested recipes contain powdered abrasives, the necessity of which I have trouble understanding. Water and ethyl alcohol should be enough to remove the kind of dirt that most frame shops will encounter when preparing picture glass.
I speculate that the intent of adding powdered abrasive is to remove stubborn dirt, but I suggest that the disadvantages of doing so outweight any advantage.
Dust, any dust is not desirable in the mat package because dust holds moisture. Moisture cause bad things to happen.
Although we have never tested the practice of introducing powdered abrasives into our glass cleaner, I speculate that it is just not possible to completely remove all of the powder from the glass surfaces, no matter how fastidiously it is wiped. Therefore, the residual powder left on the glass after wiping will remain inside the mat package, to eventually fall as dust onto the artwork.
While dry calcium carbonate may be less harmful to artwork than some other chemicals, it's dust will eventually collect moisture, running the risk that it may become chemically active with the art medium.
Of greater concern is rottenstone, which is made from sulphur-bearing volcanic pumice. The dust may react with atmospheric moisture, to produce sulphuric or sulphurous acid, which is bad news for art.
. . . so I question the wisdom of adding powdered abrasives.
[This message has been edited by Orton (edited March 13, 2001).]
