Nigel,
I think the biggest problem with disposable bottles, which is why I would always advise against them, is the fact that as the gas evaporates the temperature of the remaining liquid falls. This is due to an overall reduction in energy of the contents as the higher energy molecules (the gas) are removed from the bottle.
Anyway the result is that as the gas is used and the temperature drops the rate of evaporation reduces and consequently the pressure of the saturated vapour drops. The big problem is therefore that the pressure of these things is not a constant and it throws out any carefull airbrushing operation completely.
A compressor is the only way to go, bearing in mind the considerations that you point out. |