im using msc for sealant... the safest sealant for resin so far. and i do read that andreja, is now using liquitex for sealant for her face up commission. search for her deviantart, youtube or blog
not sure that its the same liquitex....
and when to use it,
give first layer of spray to the blank face before you painted or blush the face.
after blushing, you can seal everry step with a spray...my recomendation is watch for andreja's video on youtube XD