Why are we seeing black "carbon like" specks in our fired porcelain crowns?

[Artexperience]

We have ruled out the obvious work space environmental contaminants. The specks are random and both surface and deep. We purge our oven appropriately, we fire shade tabs directly from the porcelain bottles and still see the same results.

 

[Car 54]

What porcelain are you using?

 

[Artexperience]

What porcelain are you using?

Noritake EX-3

 

[rkm rdt]

It's metal !

 

[DevonR]

We were fighting this problem a while back. We hired some company to clean our furnace ducts and have noticed a big improvement.

 

[Car 54]

EX-3 is a good stable porcelain. Have you tried firing some tabs in a different oven?

 

[Artexperience]

I also see

We were fighting this problem a while back. We hired some company to clean our furnace ducts and have noticed a big improvement.

Good to know.

 

[Artexperience]

EX-3 is a good stable porcelain. Have you tried firing some tabs in a different oven?

We are a small lab, we have only one oven.

 

[Artexperience]

It's metal !

Not thinking it's metal, only because we were able to slightly "smudge" the black speck (which was on the surface) with a fine instrument, the speck looked undefined afterwards, using a loop to see.

 

[Car 54]

Do you have a different porc system in the lab that you can fire some tabs with, and see if it happens with that, then Devon may be on to something? Something got moved, disturbed, filters changed etc. Trying to figure out when this started and what it may have coincided with?

 

[Artexperience]

We were fighting this problem a while back. We hired some company to clean our furnace ducts and have noticed a big improvement.

Just to be clear, you are talking about the furnace ducts to the firing oven, correct? Not your heat source?

 

[Artexperience]

Do you have a different porc system in the lab that you can fire some tabs with, and see if it happens with that, then Devon may be on to something? Something got moved, disturbed, filters changed etc. Trying to figure out when this started and what it may have coincided with?

That's the troubling part.......it happens in spurts. We can go for weeks with no seen problem, then it's days of frustration grinding them out and spending extra time on units. In typing this, I realize it's probably NOT in the porcelain if it's not every time. Hmmm......

 

[rkm rdt]

Not thinking it's metal, only because we were able to slightly "smudge" the black speck (which was on the surface) with a fine instrument, the speck looked undefined afterwards, using a loop to see.

We had exactly the same problem with the same porcelain.

 

[Artexperience]

So the heat source ducts and filters?

 

[Car 54]

We had exactly the same problem with the same porcelain.

With EX-3?

 

[Car 54]

That's the troubling part.......it happens in spurts. We can go for weeks with no seen problem, then it's days of frustration grinding them out and spending extra time on units. In typing this, I realize it's probably NOT in the porcelain if it's not every time. Hmmm......

Unless it's in a C-2 you do every so often, or a enamel for certain shades?

 

[rkm rdt]

yep! When the specs are internal then you have a dirty environment.

 

[DevonR]

Just to be clear, you are talking about the furnace ducts to the firing oven, correct? Not your heat source?

No. The furnace ducts that heat and air condition the lab. Gotta keep your environment clean. Wipe the dust off everything in your porcelain room and in and around your porcelain oven.

 

[Artexperience]

Unless it's in a C-2 you do every so often, or a enamel for certain shades?

We'll have to make a note, keep a log of sorts to see if this is the case.......thanks

 

[Artexperience]

No. The furnace ducts that heat and air condition the lab. Gotta keep your environment clean. Wipe the dust off everything in your porcelain room and in and around your porcelain oven.

We are currently cleaning the air conditioner. thanks, we'll see.