Black Flecks On Kiln Shelves

[AnitaMarie]

Hi - I am new to firing my own kiln.  I have an old manual Cress kiln that I have used 4 times now.  I put kiln wash on my shelves each time and I after the last glaze I noticed that there are little dark flecks all over the shelves.  Is this glaze that needs to be ground off?  Or is this just something I put more kiln wash over?  I appreciate your help!  Thanks - Anita

[bciskepottery]

Any chance you are using glazes with cobalt as an ingredient? Some cobalt glazes can spit. I believe it can also happen in glazes with high concentrations of borax/colemanite. Just be careful what other wares you put next to spitting glazes so you don't end up with dark flecks on your white teapot.

 

Chances are the flecks on the shelf do not need to be ground off until they affect an item in firing or leave a mark on a foot-ring. Avoid excessive layers of kiln wash. I have little flecks on my shelves and they do not seem to be a problem.

[AnitaMarie]

 Not sure about the cobalt...Could be.  There were some blue glazes.  I'll do some research and let you know.  Thanks for the lead!

[MatthewV]

I am going to guess they are mostly near the thermocouple.

 

 

All kinds of things blemish a clean shelf. Many are nothing to worry too much about but be vigilant about droplets of glaze.

[glazenerd]

I will assume your kiln wash is mixed by your supplier. Which means it has a high probability of being 50/50 EPK and alumina: which would put iron spots on the list of possible suspects.  You now have 4 coats of it...

 

Nerd

[neilestrick]

I will assume your kiln wash is mixed by your supplier. Which means it has a high probability of being 50/50 EPK and alumina: which would put iron spots on the list of possible suspects.  You now have 4 coats of it...

 

Nerd

 

I respectfully disagree. Commercial kiln washes are typically high in silica, because it's cheap. Much cheaper than alumina. They keep the alumina content to a minimum to save money. And I would not expect EPK of silica or alumina to have iron particles in them large enough to leave black spots on the shelves. I have used all three in my wash for  two decades and have never had spots. It's probably from glazes, or from the elements or bricks. Whatever the source, they are nothing to worry about unless they're sticking to the bottom of your pots.

 

Can you post pictures of the spots? Are they on every shelf? All over the shelf, or just near the edges?

[Mark C.]

I agree with Neil on the 100%

The commercial washes never use much or any alumina.My homemade wash never spots with EPK and alumina 

The only possible way is rust, corrosion from thermocouple (not in protection tube) or glaze spits-my guess is glaze spits

This is where a photo would really help.

[oldlady]

this sounds suspiciously like the problem i had last year with my kiln.  the band of metal around the top and the handle were rusting, corroding whatever it is and dropping into the kiln with each closing of the lid.  my camera worked but the computer was not right for several days and i could not send pictures.  i could not even stop the capital letters from happening when i typed.

 

any photo of the "problem" would look exactly like pepper being sprinkled on white paper.  if that is something a technician cannot picture, he/she is in the wrong field.  being told that things were falling through the lid because i mentioned a hairline crack was insulting and unnecessary.  being yelled at by the owner was worse. this happened for a very long time before i noticed what it was.  tiny black specks in glaze or on shelves.  

 

i now wirebrush the lid when it is closed and rub it with some denim from a pair of old jeans.  the dust does not happen anymore.  a piece of paper on the top of the wall works well, too.  i remove it as the lid goes down.  very little speckling.

[neilestrick]

OP says it's a manual kiln, so no thermocouple to shed, although the cone supports and sitter rod can spit a little, too, but not nearly as bad. That's why I was wondering where the spots were located.

[GiselleNo5]

Good to know! And timely--my next firing will have some cobalt glazed pieces, so now I will watch the placement! 

 

My friend used to put her pots so close they were almost touching. She had some blues and teals that would spit on any lighter colored pieces nearby with a "blush" of blue. If it had been all over it would have been pretty but in just one spot it became a glaze flaw. Now when I load the kiln, I focus less on packing every available inch and make sure all glazed pieces have enough space to pass my hand through (about half an inch of space) although I do occasionally put two pieces of the same color closer than that. And I never have problems with spitting even with my darkest glazes.

[Mark C.]

This must be a cone 6 issue more than cone 10 reduction??

I pack pots as close as possible and only rarely have any of this-usually a straight cobalt blue or a copper red.

In hundreds of cubic foot loads its very rare.

Any thoughts on cone 6 doing this more than cone10?

[neilestrick]

I use a lot of blue glaze, and never have issues with it affecting neighboring glazes, and I pack them very close. I think it's all about the specific glazes, not cobalt in general.

[glazenerd]

 

Neil said- Commercial kiln washes are typically high in silica,

 

 

Nerd said- assume your kiln wash is mixed by your supplier.

The assumption would be it is properly mixed: but that is an assumption. Easily enough to spread a teaspoon dry on a shelf: see if it spots in the next firing. Which would mean there is more than just EPK involved;

 

Nerd

 

I respectfully disagree with your respective disagreement. ---say that real fast five times 

 

I noticed that there are little dark flecks all over the shelves.

that strikes me as being more than just glaze spitting, but not impossible either. If it was spitting that much, are the other pieces reflecting that as well? Or all of them have the same glaze? Pictures would most certainly help.