I think the material itself does literally become transparent. It's just that the rough surface makes it look white (see: https://en.wikipedia.org/wiki/Frosted_

I think the material itself does literally become transparent. It's just that the rough surface makes it look white (see: https://en.wikipedia.org/wiki/Frosted_glass https://en.wikipedia.org/wiki/Frosted_glass). Just like you can make frosted glass look transparent by e.g. putting some clear scotch tape over the surface (https://i.imgur.com/GZLOfbR.jpg https://i.imgur.com/GZLOfbR.jpg), you can restore the transparency of the wood by filling the gaps with resin.