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Black smoke coming out the flask during burn out


I am getting into casting and I did a few siccefull runs already. Yesterday I had to cast the 3D solidscape wax and wos doing 5 hours burnout I noticed flames coming out my kiln. I opened and noticed black smoke coming out the sprue hole. Investing the flask was not going well at the beginning, investent hardened too fast before I could do final vaccum. It was too hot in my garage!!

Any idea why this could be possibly happening?

Thank you


Just a guess, but your burnout cycle is probably both too hot and too fast. If you can get an MSDS for the specific resin, it will provide melting and oxidation temperatures of the particular resin / plastic.

You want to get the material to melt and flow down out thru the button hole. It might take several hours. You also want to do it slowly so that the chemistry of the resin doesn’t expand to much and also compromise the investment. The coefficient of expansion is higher for plastic materials than for wax. It’s also acidic on the investment.

There’s no exact science, but I would slow down your burnout cycle. Once you slowly it to 200-225 or whatever the MSDS indicates, let it cook for 4-6 hours. Then do several more hours for the regular ramp and hold cycle. I’ve noticed fumes will after that 5 hour point a couple of times, so slow you go. You’re probably looking more at an 9-12 hour burnout to end up at 1200F with a couple hors holds at the top temperature. Big temperature swings / fast ramps should be avoided.

I’ve played with ultra thin styrene sheet with some success. It’s one reason I invested in my own studio, to precisely control the burnout cycle which I discovered was crucial to a design’s success.

And you might want to use an investment engineered for platinum. It’s alot stronger in the burnout cycle for more resinous plastics.

And because the fumes are nasty, a ventilation exhaust to get fumes controlled and properly vented.

Did you try casting the flaming flask? It might be ok if you redo the burnout at a much slower ramp and hold. I’ve had flasks go freaky on me a couple of times and I let them cool overnight and redid the burnout with success. Was your job damaged?


Thank you. I trashed the flask cause initially i was going the wrong way with investment hardening way too fast…I used the same cycle for a few previous castings with success though

Also, if you’re mixing investment in a hot studio, you might try using colder water to counteract the acceleration the ambient temperature may have on your set time. We always use room temperature water, but then room temp is around 70°F. Plastics do require very long burnout schedules with slow ramp/hold cycles. Make sure you have adequate gates and sprue channels for the configuration and size of your piece too. That is an art unto itself!

Good Luck!

Ruthanne Robertson
Bench Jeweler Team Lead
Leagacy Touch, Inc.

I’ve had wax smoke severely if I ramp up past 300°F too fast and as soon as I opened the kiln door (Paragon SC3), it caught fire as soon as the oxygen-rich air entered the chamber.

Sooo, I have my hour of 300°F with the button upside down to catch the melted wax in the pan, remove the pan from the kiln and them let my kiln ramp to 700°F before it heads up to 1400°F to remove my resin.

No ventilation system? Smoke from wax burnout is pretty normal. How much and what type depends on the wax. Usually vented out of the kiln and into the system. I guess the best way to avoid it is to melt it out low and dump it or use a steam dewaxer. We usually set the stinky part of burnout for overnight and the casting would be ready to go in the morning.