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estebanana -> RE: Pumice alternative (May 11 2015 0:25:05)
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The thing about fillers is there are two basic ways to go:
One type of fillers where the substance can be rendered semi transparent when it is wetted by which ever 'glue' you use to stick it in the pores.
The other is filler than stays opaque and does not reflect light through it.
Pumice, chalk, calcium carbonate, etc will become partially transparent if used well and it allows the refractive index of the wood to remain high. It means the light entering the wood will penetrate through the pore filler and reflect back out from a deeper layer in the wood. Keeping the refractive index high in this way creates deeper looking finishes.
Using the opaque fillers, wood dust, acrylic, microballoons with resin based mediums make an opaque barrier with lowers the refractive index. It makes it more difficult to get deep looking finishes.
Rottenstone is also fairly opaque, but the gypsum, calcium carbonate, cuttle bone, pumice, white marble dust, can all be semi transparent when they are saturated with shellac.
But it depends on how you like the finish to look, sometimes wood dust is good looking, sometimes pumice, to an extent it also depends on the kind of wood you are working with and the wood color.
It all works, but just be aware that different pore filling materials effect the look of the finish in a subtle way. The other day I used ebony dust to pore fill a section of head stock that I wanted to be dark...then I used pumice on the body. You can use different pore filling materials on different parts of the guitar to great effect.
Refractive index is a big subject but here's kind of how it works in pore filling.
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