Celadon grey glaze firing with no colour

[Rosie M]

Hello, I hope I might find some advice here - I am using a pre mixed glaze powder, staffordshire stoneware 'celadon grey' firing to cone 9, but it has come out completely transparent with only a slight amber/cream in a few little places where thick. Glaze seemed a good consistency and clinged to the pieces nicely when dipped. If it helps, in the same firing I had a few pieces come out very brown that should have been quite blue.  Very grateful for any pointers, Rosie 

[Bill Kielb]

What comes to mind is it was fired beyond its range somewhat. Often as one fires hotter, color changes or cannot be retained. It would be nice to know what cone you actually fired to as rate of firing in the last 100c really  influences the maturity more than a peak temperature with a hold. Did you have witness cones in the firing? 1260 c looks like the very top end for this glaze as advertised, so I believe it likely changed from expectation due to temperature. If you research maturity, eutectic, Orton, Seger, (Heatwork) you can add to your understanding of how ceramics generally reach maturity. Artists who want a very specific color will often progressively fire their test and find the peak temperature when the color begins to fade. Knowing heatwork often enables them to retain their color by firing at a lower temperature but holding to increase the heatwork till maturity.

[Rosie M]

Hi Bill thanks for replying, the recommendation for this glaze is 1200c with soak or 1260 with short soak, so I went for the latter, but I didn't have witness cones in. Unfortunately I don't own my own kiln, I use a  studio with kilns in place and the owners operate by charging per firing, so I can't afford to do many tests. 

I noticed that pieces glazed in the celadon that were at top of the kiln retained more colour (although still not grey - a creamy colour with a few Amber crystals) whereas the pieces in the very bottom were the ones with no colour at all.  I'm still very much learning when it comes to glazing and firing so not sure which bits of info might be useful! 

Thanks R

[Bill Kielb]

Sounds like the glaze is a bit temperature sensitive. Items at the top of a kiln are often fired cooler than the middle because of the extra heat loss through the lid  and limited amount of elements that can be seen by the wares as most of the heat is radiant later in the firing . It’s customary at some studios to place witness cones throughout  the kiln just to keep an eye on how even they are firing and at some point when the elements need changing. Certain Loading / shelf combinations can affect this as more pieces are in the shade if you will. So if all true, this glaze is likely color sensitive at top firing temperatures. When one has  little control over the firing it’s often good to include a couple small test tiles of potential upcoming colors to help give a better idea of future performance.

[Rosie M]

Thanks so much for your advice Bill, really helpful, I have ordered witness cones and will try firing that glaze at a lower temp with tests. Would you recommend trying to re-glaze the pieces that haven't worked and refire? I have reglazed a few pieces before with good results. 

Thanks R

[Chilly]

23 hours ago, Rosie M said:

recommendation for this glaze is 1200c with soak or 1260 with short soak,

Depending which style cones, and rate of temperature increase, ^9 could be too hot.

 

 

[Bill Kielb]

2 hours ago, Rosie M said:

Would you recommend trying to re-glaze the pieces that haven't worked and refire? I have reglazed a few pieces before with good results. 

I never have been successful with reglazing actually. My go to if I really want to save something, I have resorted to down firing them with a suitable lowfire glaze.   That has proven  mostly successful for me. Refires never seem to work out. There are folks who successfully refine though.

[Hulk]

Clay body can influence glaze colours a bit, or a lot, depending.

Fuming from nearby ware can impart a bit of colour/sparkle, also the side directly facing the elements sometimes looks a bit different, likely due to heat variation, per Bill's point, to which I'd like to add that cooling rates also vary, depending on location in the kiln, which can influence colour and/or crystal formation... 

[Callie Beller Diesel]

I notice on the glaze description on the Sheffield site that they state it’s not a fine porcelain celadon. That leads me to agree with Tom, that clay body could be a factor here, as well as application thickness. It’s hard to tell from a picture on the internet, but it looks like the grey celadon is more grey where thinner on the single dip side. I wonder if you just need to fine tune the specific gravity on these glazes to get you desired effect.

[Min]

On 11/21/2021 at 2:28 AM, Rosie M said:

Glaze seemed a good consistency...

I would make up some tall test tiles then measure the specific gravity of both the blue and gray glazes. Record the specific gravity, do a search if you aren't familiar with how to do this. Dip 2 test tiles in each glaze once then when the sheen comes off it dip the top half of the test test tile a second time then when the sheen is off that dip one of the top corners a third time. Glaze at least 2 test tiles with each glaze. Keep one test tile of each glazes unfired. Fire the others, scatter them in the kiln so you can see any difference placement makes. Once fired see if the single, double or triple dip looks best then scratch through the unfired test tiles to see glaze thickness which will be what you aim for going forward along with keeping a consistent specific gravity.