well, I tried glycerine and am not impressed yet.
True, it's less than half the cost of the Wintergreen oil I got...
First glycerine experiment:COLD, paint it on, rub it in. No quick useful result that I can see except slippery. Slippery is good to fit onto a carb but that's not the point here.
Next, the boot went into a glass jar with just glycerine
liberally applied (but not swimming in it). The jar then went into boiling water. The glycerine did not vapourise like the WO, but some droplets were condensed in the jar with the lid on loose... maybe just atmospheric water?
No particular strong smell-a plus, if you don't like "spearmint flavour"
This was a disappointing test. It was wonderfully soft and a bit greasy when still warm, but at my room temperature (60F!) it went back to being hard as a rock, as it was originally.
It was not as good as the wintergreen using the same no-water ,no-solvent process.
Or even as good as WO, painted onto a Cold boot.
The above method is a fail for me.
BUT,
Next, I added water to glycerine just covering the boot in the jar and heated the jar in a pot of water to open boil until the pan ran dry- a better result, when cooled to room temperature....
So, Out in the shop, I tried jamming them each onto a cold carb. The wintergreened one went on albeit with hard pushing, but the glycerined one was just too hard for this mortal, though less hard than it was in it's pristine and aged state....really rock-hard rubber. Sounded like a marble hitting the floor...anyways,
The wintergreened one is definitely softer to the feel, despite being cooked two weeks ago.
There is no swelling once cooled from my "double-boiler" method. The lack of swelling that others mentioned may point to a failure in my method.
Neither is yet as "permanently" soft as when the rubber is new, or as soft as when warmed with hot water or a heat-gun.
I have not tried the simpler
open pot and water method. Water
is a good solvent....
to refresh, SVSooke and jabcb have tried "Rubber Renue"
http://www.thegsresources.com/_forum/showpost.php?p=1944794&postcount=22
It has the advantage of being applicable
in situ without a heat gun or kitchen laboratory so would be a good precaution to apply it before removing carbs off old bikes. Meanwhile, I so far think I will heat-gun 'em
and use WO because that also gives some result in that instance where I don't expect to just buy new boots.
A bit of glycerine splashed around won't hurt either. Slippery stuff on rubber.