PVA Glue

PVA glue is used frequently in modelling, it's transparency drying abilities are fantastic, but it's the versatility of it when watered down that offers much more. I use between one quarter to a third PVA to water, and a squirt of washing up liquid, shaken and stirred. Put it in a washing-up liquid bottle and it'll last for months, give it a stir and a shake from time to time, when mixing I tend to use warm water.