Hi Lin, Bathtub caulk should work. However, it might be a little
difficult to position in tight locations.
Another product that would probably work a little easier is rubber
cement. The type available at most office supply stores. It’s a little
thinner than bathtub caulk & could be placed with greater accuracy &
ease. It is also easier to remove & I think there’s a thinner
available for it, if required.
The purpose of the resist used in sand/bead/abrasive etching is to
absorb the energy of the individual particles. Products that have the
adhesiveness, toughness & resiliency of rubber work quite well.
Products that are hard, tend to be abraded by the etching agent just
like the work piece. The degree to which they are etched is dependent
on their hardness relative to the hardness of media & the air
Most of the companies that make & market grave stones use a thin
rubber sheet to mask the uncut areas of the stone. They usually use a
carbide grit sprayed from a industrial sized spray gun & compressor.