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Old 04-22-2021, 11:51 AM   #3
JoeCedar
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Join Date: May 2006
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If the varnish is sticking to the container, what harm is is doing? Does it flake or fall off easily? Why not let it stay where it is? It has been there for years. Do you think it will suddenly redissolve and cause problems with your stove when you add new fuel?

Before I became a serial hiker, I was a chemist specializing in solubility. Some pertinent points to consider:

* What is the varnish, and what does (does not) it dissolve in? Paint thinner does not make sense since it is also a non-polar hydrocarbon like the fuel (from which the varnish went to the container surfaces). Beginning chemistry students are always taught "like dissolves like".

*It would be better to try a solvent unlike the fuel or varnish such as an alcohol (methanol or denatured ethanol) or ketone (like acetone). Unfortunately, these solvents are more difficult to find due to environmental regulations (and you are stuck with a full container if it doesn't work).

* Aqueous materials like acid or alkaline chemicals might react and dissolve the varnish but they should be avoided because of their potential for reaction with the aluminum container. Chlorine bleach is great for coffee pots for example. Aqueous household cleaning agents such as a dishwashing detergent can be a good cleaner for oily residues, but the evidence suggests that the varnish is not an oil since it would not have separated from the fuel in the first place.

*The hydrocarbon fuel itself is a petroleum distillate which is very chemically stable (mostly free of additives, unlike gasoline which is loaded with stuff). The varnish may be an impurity in the fuel or more likely the result of degradation/reaction of fuel or impurities by pathways such as oxidation or polymerization. If the varnish is a polymer it may be very difficult to remove without using something which would damage the aluminum of the container.

* Heating the container in an oven, preferably without fuel, might cause chemical or physical change to the varnish. If it dries and flakes off, you might be worse off. The hope is it converts to something which can easily be cleaned out.

After considering and doing all this, if you are still concerned about possibly harmless varnish on your container, you will probably choose the "nuclear option": throw the bottle in the trash and buy a new container.

Enjoy your experiments!
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