Gas bubbles in porcelain

[charles007]

Sorry Artemis, I was joking in a light hearted way when I used the name Willis, many of us grew up watching the TV show Different Strokes.......
Your English is quite good.

I grew up firing near or at 1050C to clean my muffle as a regular maintenance program years ago . What exactly does "Purge All" do since you know a lot more than I do about cleaning muffles?
I've never seen a group of crowns, 2 or more gas, even though I've worked in 3 different in-house labs and in my own lab for more years.

Its kind of hard to remember back years ago, I thought firing to 1050 with carbon was to prevent greening from silver alloys.

I thought gassing came from contamination, which mostly comes from dirty crucibles, cross contamination of grinding stones-NP to precious, bad techniques in metal finishing-trapping particles, moisture in air lines, natural gas, extreme high setting in your propane/oxy mix.

We frequently hear about labs having gassing, and for the most part, they are having multiple units to gas. I think it has more to do with crucibles and metal finishing than anything else. If the oven is where the gassing is coming from, it would be impossible to glaze any crowns without bubbles.
Please correct me if I'm wrong.
What say you.
Charles

 

[odchamp]

We had problems now and again with bubbles, but when we switched to an induction machine using ceramic crucibles they went away.
From my own personal opinion I would never go back to torch, but it's what you know trust and believe in.
What we liked was the cleanliness of castings and the ease of use, no gas bottles etc, etc.

 

[sixonice]

i agree with the last part of charles reply. in all the experiences i have had with gassing, it most always can be attributed to improper metal finishing. if i have gassing the first thing i'll do is strip the glass and start from scratch with metal finishing, being careful to do this correctly. 99% of the time this takes care of the issue. the only other thing i have done when re-metal finishing did not take care of the gassing was I scrapped my buttons and started with a new fresh crucible and new alloy (i attributed dirty/burned up button to be the cause there).

 

[subrisi]

When you finish the surface of the restoration with carbides, you can "smear" metal over micro voids, trapping air in it that tries to get out and creates bubbles. To avoid this, grind over the whole surface with a pink stone slightly to open these "traps". Go only in one direction, sandblast ans steam clean before degassing. If I don't (forget) do this step, I always get rewarded with bubbles.
Angelika

 

[ZOOMAN]

Check you vacuum, level settings, leakage, weak pump. if your vacuum level is set too low, does not pull fast enough, is weak or leaks this could exacerbate or even cause the problem.

Contamination can accuumulate for lack of vacuum, turning off the furnace at night, low idle or night temperature.

You might want to do the following:

Before you put any type of purging chemicals in your furnace:

1. Test your vacuum
2. If you vacuum is good, run a high temperature program with vacuum all the way through the cycle (1050C - 1100C) hold for about 15 minutes, then let is cool down to the idle temp and run it again.
3. A tab check your translucency

If all of this comes out ok, then I doubt the furnace is to blame:

Metal, water, environment...

 

[ZOOMAN]

OOOPPPS! - Proof reading is important!