I use baking powder in my micro sand blaster for cooked artifacts. It is abrasive enough, smaller than 5/1000s probably closer to 1 or 2 thousands and you can see your progress as its being cleaned. If you try this technique, start with the tip away from item being cleaned and slowly get it closer until you see progress. You can back the tip off slowing the amount of pressure and abrasive giving you control. If any one tries this, use a old penny to give you an idea of the removal rate dictating the pressure used and also starting points. Keep the tip a constant distance once you find it giving you a nice even cleaning. Remember the key word, micro abrasive. Arty