Since gases mix over time, regardless of which gas you use the important determinant would be the quantity of inert gas you add relative to the remaining oxygen content. It would seem to me that other than the fact that propane/butane is easy to compress into a liquid inside a consumer type aerosol bottle, it would be advantageous only to the extent that injecting it in a bottle at the gas/liquid boundary could momentarily form a layer that would push the lighter air out of the top of the bottle. This would only work if you use a thin tube to inject the propane/butane at the liquid boundary and manage to do so without causing significant mixing flows within the bottle. Whatever boundary you introduce would dissipate over time, at which point the remaining air will mix with the inert gas. Tetenal Protectan comes with such a tube but how well it works is anyones guess. Tetenal claims you can witness the exclusion of air by hearing a change in the sound exiting the bottle. I never found this to be obvious enough to use as an indication and simply resorted to the method of injecting enough to cause 3 or 4 changes of atmosphere thereby statistically reducing the oxygen content. If I could find a cheap bottle of nitrogen gas I could do the same with much less fear of using flammable gases. Something tells me I'll never see another bottle of Protectan anyway, so next time I'll probably buy a can of something different.
Denis K
