OH YEAH... I left out a step.
I let them air out for a couple days before the toaster.
Important step! Thanks for pointing out my important omission. Seriously. I kinda take my knowledge of this kinda stuff for granted and shouldn't... just been working in the refining industry for 23+ years and it's second nature.
I happen to be fairly familiar with hydrocarbon flammability curves, and you bet... acetone is super flammable. Proof: fingernail polish is usually acetone, and you can dip a Q-tip in and light it off. It burns hot and clean, very little smoke (poor a puddle in the driveway, no cloth or paper, and carefully ignite in the driveway for proof... er, I mean, don't try this at home folks!)
The ignition temperature of acetone is 869 deg F, and while I ran the toaster at 180 deg F the first time, and then lower at 140-150 degrees the second time, the heat coils (bars) probably run pretty hot when they are in the "on" cycle of the toaster. Perhaps hot enough to ignite acetone IF it's concentrated enough in the toaster. Hence, dry them out first.
From wikipedia:
The most common hazard associated with acetone is its extreme flammability. It
auto-ignites at a temperature of 465 °C (869 °F). At temperatures greater than acetone's
flash point of −20 °C (−4 °F), air mixtures of between 2.5% and 12.8% acetone, by volume, may explode or cause a flash fire. Vapors can flow along surfaces to distant ignition sources and flash back.
Static discharge may also ignite acetone vapors.
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This is actually a pretty low concentration of hydrocarbon in air compared with other heavier hydrocarbons. Similarly, gasoline is 1.4% to 7.6% range, so acetone requires a bit more concentration but not much, but this puts it in perspective. Diesel is lower at 0.6% to 7.5%, but that doesn't tell the whole story. Acetone and gasoline are "flammable" as the flash point (temperature at which vapors evaporate) is much lower than diesel (-17C for Acetone, -40C for gasoline). Technically, Diesel is combustible, as you have to get it warmer (typically above 140F) before enough vapor is given off to become flammable.
This is a good overview:
http://en.wikipedia.org/wiki/Flammability_limit
Acetone is quite volatile, and if you let wood soaked acetone air out for a while (much longer in cold temperatures, or do it in your basement if you are blessed with a basement), nearly all of it evaporates, and fairly quickly.
2.5% volume in air doesn't sound like much acetone, but that amount would smell strongly. HOWEVER, I
can't say that I recommend this toaster procedure to people who don't really understand what they are doing. Just for the record.
Probably shouldn't have posted it since some fool will F@$& this up and burn his face or arms, the same guy who cleans the floor in his garage with gasoline, and then wonders why his garage blew up (hint... pilots on gas water heater MIGHT be an ignition source... or maybe it was static electricity?).
Back to Thuya burl... the procedure outlined above did not result in any cracked blocks. The blocks were all about 1" square by 5" long.
