The bottles (glass?) should be good for storing small amounts of any kind of hobby materials that have solvents or other chemicals that are bad news for plastic containers. I actually still have a few old baby food containers for that purpose from when my kid was little. The only catch is that the lids need to be in good condition, otherwise the harsh chemicals/ solvents will still slowly evaporate and escape (which may be why the paint hardened in the first placeā¦).