Assessing the results of my 1st Glaze firing

[liambesaw]

I don't sieve every time, only when it's been a few weeks or longer since I used it, or if I can feel or see chunks when I'm mixing.  For small quart sized test batches I sieve them every time, because I have a test sieve and it's very quick.  Home Depot carries lidded quart sized plastic paint containers that are AWESOME for this, and the talisman test sieves fit exactly inside of the rim.  WHAT A DREAM!  Wish the talisman 5 gallon bucket size sieves were a bit cheaper because my cheapo plastic 80 mesh sieve is kind of a pain.  Maybe when I'm rich, because that rotary sieve is soooooo boss.  Maybe your studio that you buy glaze from will let you sieve your glazes with their rotary sieve.

[shawnhar]

Thanks Rae, I took the glaze down to the studio and sieved it, nothing wrong with it, no chunks, was told it's my fire, not the glaze.

Thanks Liam, I'm sure they would.

 - So, I am completely lost now. Refiring made all of the pitting/blistering/pinholing worse, WAY worse. The first attempt fired over (cone 6 w/10min hold) and has problems but is a lot smoother, the second batch fired to cone 6 (5 w/15min hold) was a complete failure, every glaze was ruined.

I have no idea what to try now, cone 6 with no hold? 

[Fred Sweet]

shawnhar-

Since your first firing was over-fired and was blistered, pinholed, it doesn’t make sense to add more heat work (by increasing your hold time) to the subsequent firing. If the pieces were refired , it takes less heat work to re-melt the glaze since all the materials were already combined in the glass matrix. If the second firing was with new unfired pieces, I would have considered lowering the hold time or the target come, since your first was over-fired.

Something to ponder.

Regards,

Fred

[shawnhar]

Thanks Fred, sorry I wasnt clear. The first firing was cone 6 10min hold, and it overfired with ^6 cone slumped down, the glazes came out dark but they were mostly smooth, some slight blistering I think and some pinholes but not too bad. Second firing with new pieces was cone 5 with 15min hold, witness cones showed ^6 bent over with tip touching shelf, they came out blistered/tons of pinholes, so I refired those again, same cone 5 15min hold , they got worse. Guess I should have tried cone 4.

I have to make a bunch of basic pieces for the next test fire in stead of wasting all my mugs on this, sucks losing them.

[Min]

@shawnhar, glaze blisters can be one of the most frustrating things to solve. There are many things that can contribute to them, bisque firing, overfiring, underfiring, glaze viscosity, speed of firing, cooling  and on and on. There is an excellent 4 part article on solving the problem here. (links to parts 2-4 at the very bottom of the page)  Yes, make up a ton of test tiles and get things sorted out with those. Put some "mass" in the kiln at the same time to slow the firing/cooling down as actual pots would do. Some kiln posts will do. 

Like has been said already I would do a thermocouple offset so your cones match your firing. If cone 5 plus a 15 minute hold is bring cone 6 down then your tc is off. 

[shawnhar]

Thanks Min, that is brilliant regarding the mass, I feel really dumb now, wasting my mugs on the second firing when I could have just filled the kiln with shelves and furniture with a few test pots and next firing will do just that. 

Set the TC offset, use furniture and shelves for mass, and use a firing program provided by dhpotter, which was based on yours and Tom's recommendations, to slow the ramp up to the final temp, let it drop, then hold.  First thing though is just do the TC offset and do a cone 5 no hold with a couple of test pots and witness cones, then go from there. Making my test pots tonight

Thanks you everyone!