what does the lighter fluid actually Do?? DOES IT ACT AS A DRYING AGENT FOR THE DAMAR VARNISH? if thats the case couldnt you use ACETONE?? Just make it 80% acetone and 20% varnish?? JUST CURIOUS
The solvent is to ensure there is a minimum of the actual medium applied to the substrate. If the medium was applied too thickly, then there would be a gummy layer to engrave through.
Different solvents have different drying rates, but with the ratio of solvent used in these transfer solutions, they're going to flash-off quickly no matter which one is used.
Acetone will probably work OK, but as dammar varnish is based on pure turpentine, you would be fine diluting it with mineral spirits/white spirits (which ever it's called in your neck of the woods).
Lighter fluid (either Zippo's new formula or any other brand that contains Naptha) will evaporate virtually instantly because it's so volatile and the more volatile the substance, the more poisonous the constituents are, so be careful.
Acetone is pretty nasty stuff though which is why I recommended using something slightly less noxious like white spirits.
The bottom line is most of these solvents contain hydrocarbons and if you can smell them, then you're poisoning yourself. It's wise to choose the least harmful.