The epoxy that I am working with is UV curable with a cycloaliphatic epoxy resin base. I am trying to reduce the viscosity. Whatever I add to thin the epoxy, it needs to be able to evaporate off so that when I cure it, it's just the epoxy remaining. I have used solvents like acetone to thin 2 part thermal cure epoxies, but I am not sure if this is appropriate for a UV cure epoxy or which solvent would be best to use.
Adding solvents that need to evaporate, to your epoxy, can cause pinholing. You need a integratable solvent. Styrene monomer works well. You can get it from a fibreglass supply or by pyrolizing poly-styrene.
The monomer will combine with the epoxy so it won't need to evaporate out of the epoxy.
You can heat up the epoxy resin to reduce the viscosity.
To make it thicker, you could add any kind of inert powder filler, like talcum, silica variants, whatever.
I understand what you want to do with the solvent - but it seems not to be in common use.
But it is worth a try with a small batch. The curing by UV makes it easier, because you have much time to get the solvent removed before curing. And you van even heat it up without shortening the workable time by it.
It is important in what shape it will be used: Is it a thin coating, or casting a complex object into a block. I assume a coating, and with low viscosity, it will be a very thin coating.
When the epoxy can wet the surface, it will find just about any pore to go into - independent of viscosity. It just takes longer if it is thick.
As for the solvents to try, Xylol and Toluol could work - evaporating quickly, but not very quickly. Try a common "paint thinner" - some are a mixture of these