How do you pick a grit size?
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A quick and simple answer is to pick a maximum grain size that is about equal to the thickness of the coating being removed. So if what you are trying to remove is 1.6 mm thick (.063 inch), you would choose a 12 grit. A bit finer size is often used as well, because you get better coverage as the finer particles fil into grooves, cracks, voids in the surface that the larger particles will not fit into.
A more detailed answer involves selecting a grit size based on the surface profile you are attempting to achieve on your substrate. A quick guide can be found here.
Keep in mind that the more rounded a particle is, the more contact area it has with your substrate, and this can speed up cleaning rates. Glass bead is a good example of a cleaning abrasive, whereas the more angular and blocky aluminum oxide particle is useful for actual surface preparation. (Where you want the abrasive to leave a surface profile for a future coating).
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Sherrie,
In your other post you asked if I tried the #18 beads. No I didn&#;t,
I just was looking at samples in some bottles so folks could decide
which grade they wanted. # 18 was very fine however.
Lowering the air pressure will usually make a &#;lighter&#; not so deep
matte surface so it would most likely easier to remove. Question,
why are you trying to get a matte finish that you are going to
remove?? Are you removing it from areas you want polished and
leaving matte in the areas you want it? Have you thought about using
a mask to keep bright areas bright? Also, using &#;air brush&#; or &#;air
pen&#; blasting units would allow you far greater control over what is
and is not getting matted. Paschaa (spelling is not correct here)
air brush company makes air brush blasters for very fine, detailed
work. I think they are about $80. Douglas and Sturgess
(800-278-) has them and I think the blasting media too. Corundum
is usually available from any lapidary supplier.
John Dach
MidLife Crisis Enterprises
Cynthia Thomas Designs
Cynthia&#;s sculptures are at: http://www.mlce.net
Maiden Metals,
If you want to learn more, please visit our website ceramic blasting media.