Help with Porcelain Bubbling Problems?

Robert Mahony Start with clean metal ,Second change crucible ,Third new casting tip. Read the melting instructions for your gold and follow a strict metal prep with new pink stones used on one type metal or carbides work well. Make sure your not trapping air in the metal. sand blasting with 50 micron aol2 . Set psi on sandblaster to about at 10 bars and clean in distilled water in the ultra sonic for 5mins....[More] do not touch your metal before or after degas(oils,hand lotions or other dirt can contaminate) Degas according to your manufactures instructions. If your using any N.P. or high content silver metals make sure to purge oven weekly with carbon. Make sure that your metal does not have strong oxides growing on the surface the copings(some is good). Calibrate both ovens burn out and porcelain. If you still have bubbles send your units into a dental gold manufacturing company to inspect your metal you could be over heating the metal or trapping investment into the metal.

Michael DiPaulo I've heard of this problem alot over the years. Bubbling is a result of surface contaminants coming from any of the following: improper finishing stones (no heatless they have metalics), use pink stones ; sandblasting using recycled ALO2, use only fresh blasting media; the soldering process can also cause bubbling, if case has been soldered then double the degas time ( in air). I recommend finishing...[More] with pink stones, sandblast with 50-60 micron ALO2, steam or ultasonic clean (distilled H2O), degas according to manufacturers instructions. If oxide is heavy or dark blast it off, steam clean , then opaque. As others have commented a slurry bake can help, however I say fire this slurry 10 degrees C higher than the opaque temperature, this should neutralize any contaminants than would react at the normal opaque temp. this will not affect bond, then apply normal opaque bake(s). One other note if you are using a paste opaque bubbling can occur if the case enters the oven too quickly, pastes are not water based and need more time to dry before firing. Also never add water to paste.
Hope this helps.

Harry Carlisle I had this problem years ago and it seemed to be running the first opaque to high. I have used non precious 99% of the time. I grind all the metal with a heartless stone then I cover it with a product called color guard which they quit making. I tried to have them start again to no avail. It will cover a multitude of sins. You would not believe how carelessI am and it still works great. I quit using...[More] gold forty years ago and all my problems went away.
A heartless stone

Curt Morgese Assuming you have prepped your metal properly I would guess you may be trying to opaque in one bake. If so try two bakes, the first being a slurry. Don't dry too quickly and do not over fire. Do the same with the second bake. Your opaque should have an egg shell finish look, not a high glossy look. Good luck!

Nancy Zhang Thank you so much

Michael Kudrna If you haven't already tried this,replace the muffle.

Flemming Behrend Stop casting with a torch and move your production to either electric vacuum pressure casting or induction. Torch casting is for jewelry and is completely unreliable!

Pete Ruberto You may try cleaning your touch tip. Looks like you can have carbon getting into the metal.Place the touch tip in white vinegar with a dash of salt. Leave it in the ultra sonic for about 5 minutes, no more because the solution will eat away at the tip. Wipe off the tip with a towel. You will see a lot of black carbon residue on the tip and INSIDE the tip come off.