any mark that will stay on top of a layer(s) of SG. a mark that won't seep through your first layer like AIO or SG and is paint safe. put it on the layer you're guarding against depletion. you now can check if that mark is there or gone. this way we don't need to hula/hope about the endurance of SG or any layer for that matter.
i :gouste: your diligence.





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