Re-Glazing Cone 6 Glazed Pieces ? ? ?

[chiefman3d]

We just did our first glaze fire in new Paragon TFH24 kiln after a test fire and bisk fire. Used the firing schedule recommended by John Hesselberth (Mastering Cone 6 Glazes) with the only modification changing the max temp from 2185 to 2200. Everything else left the same as far as ramp up and cool down.

 

Several of the glazes from his book did not turn out as expected and i ask him about them, with a response that he thought the kiln may have fired to ^7 instead of ^6 based on what I told hem and the photos I sent. The other problem was I used granular rutile instead of powdered and substituted zircopax for tin oxide. I did not have test cones in place and was relying on the digital readout from the controller, which he said I should not have done. All of those things are fixable for future firings. Sorry for the long start of this, but I felt it important for you all to know what drove my question.

 

Assuming it over fired, the other unexpected result was a total change in "Pete's Weathered Bronze" and "Oatmeal Rust" which my wife uses for her fish sculptures. All the pieces in this load looked burnt. The oatmeal rust fired in our older kiln with kiln sitter at ^6, when used over a white or buff colored clay came out a nice solid cream color. This time there was a lot of rust splotches on the sculpture faces. The weathered bronze was really bronze with very little copper verdi green, which we have been getting all along. I have attached photos to see what I am talking about.The Monk fish is the way both the face and tail normally come out.

 

 

Finally my question....... In trying to save this work, is it possible to re-glaze these pieces with the same or a lower fire glaze and re-fire them to a lower temp (which we would probably do in our older kiln, since we know what the result would be based on it's firing history? Or will re-firing them at the lower temp change the glaze that is already on them back to what it should be? That would be great if that worked!

 

Thanks for any help anyone can give.

 

Craig

[GEP]

Craig,

 

Here are my thoughts, they don't address all of your questions, but I'm sure others will have more thoughts to add:

 

Years ago at the center where I teach pottery classes, someone once bought granular rutile instead of powdered rutile, and it screwed up a bunch of glazes (all cone 6 ox). In some cases it resulted in brown blotches similar to yours. Rutile is both a colorant and an opacifier, so switching to the granular form will change both. So I would add some powdered rutile to your shopping list, along with tin oxide and witness cones.

 

I agree with John Hesselberth that your latest pots are overfired compared to your previous pots. Question for you ... were you using witness cones in your older kiln? It's possible that you were firing lower than cone 6, even with the kiln sitter. If you hadn't measured it with witness cones in a while, I think your next firing should be in your old kiln with witness cones. Then use those cones to decide how to program your new kiln.

 

I don't think you can reglaze or refire the overfired pots ... sorry! Oh, the joys and pains of having a new kiln.

 

Mea

[Tom]

Hi Graig

 

I have refired a lot of pots in my day, I teach children. one thing is the adding the same temperature of glaze over an entire piece is usually a disaster. The glazes almost always run or move more then you like. You can use a low fire (cone 06 or about) many commercial low fire glazes will brush over fired glazes. Then re-fire then at the low fire temperature.

 

As for your new kiln with a computer. Fire it with witness cones watch the cones through the peep holes, chart them as to when they fall and at what temperature the read out says. I found that with mine the witness cone and the temperature were about 2 cones off the cones were dropping before it reach the temperature. Learn where the cones meet what temperature and use that temperature. Test it often your thermocouple is going to burn down a little on each firing which will change the read out temperature.

 

Tom

[chiefman3d]

Craig,

 

Here are my thoughts, they don't address all of your questions, but I'm sure others will have more thoughts to add:

 

Years ago at the center where I teach pottery classes, someone once bought granular rutile instead of powdered rutile, and it screwed up a bunch of glazes (all cone 6 ox). In some cases it resulted in brown blotches similar to yours. Rutile is both a colorant and an opacifier, so switching to the granular form will change both. So I would add some powdered rutile to your shopping list, along with tin oxide and witness cones.

 

I agree with John Hesselberth that your latest pots are overfired compared to your previous pots. Question for you ... were you using witness cones in your older kiln? It's possible that you were firing lower than cone 6, even with the kiln sitter. If you hadn't measured it with witness cones in a while, I think your next firing should be in your old kiln with witness cones. Then use those cones to decide how to program your new kiln.

 

I don't think you can reglaze or refire the overfired pots ... sorry! Oh, the joys and pains of having a new kiln.

 

Mea

 

 

Hi Mea, and thanks for the reply,

I have already added those to my shopping list and will have them next week.

 

As to the old kiln, Yes I was using witness cones stuck into a small strip of clay. ^5, ^6, ^7...in a row and the 5 bent as it should and the 6 just slightly and the 7 never. This is with a 6 in the kiln sitter and it kicked it off. I used a kiln sitter calibrator tool to check the required gap and movements and it was right on, but apparently the temp there vs. down throughout the kiln was very different.

 

I will have to wait till the new cones come in ( the larger self supporting ones) to test the new kiln. We attended a workshop at Highwater Clay in St. Pete, Fl. in Jan. and Jim Skutt was one of the speakers. (If anyone ever gets a chance to attend a workshop where he is speaking, don't miss it. Hi has a wealth of knowledge and a very engaging speaker.) Jim said he did not recommend sticking the smaller cones in clay because of the inaccuracy of placement in both depth into the clay and the angle with which they are designed to slope. That is why he recommends the self supporting larger cones

 

Thanks again and I will keep trying till I get it right

 

Craig

[chiefman3d]

Hi Graig

 

I have refired a lot of pots in my day, I teach children. one thing is the adding the same temperature of glaze over an entire piece is usually a disaster. The glazes almost always run or move more then you like. You can use a low fire (cone 06 or about) many commercial low fire glazes will brush over fired glazes. Then re-fire then at the low fire temperature.

 

As for your new kiln with a computer. Fire it with witness cones watch the cones through the peep holes, chart them as to when they fall and at what temperature the read out says. I found that with mine the witness cone and the temperature were about 2 cones off the cones were dropping before it reach the temperature. Learn where the cones meet what temperature and use that temperature. Test it often your thermocouple is going to burn down a little on each firing which will change the read out temperature.

 

Tom

 

 

Thanks for the reply Tom,

 

Please read the reply I did to Mea's post about cones.

 

As to re-firing the pieces, The Weathered bronze is the most important, which is a cone 5-6 so I am thinking of re-glazing that part of the pieces and firing it in the old kiln for now and then getting a cream colored 06 glaze to re-do the faces in a 3rd fire. Lot of firing, but there is a lot of work in the pieces as well and hate to waste them. I know, "it is only clay" to quote Steve Booton. http://www.youtube.c...vebootonceramic

 

With the new kiln and the peep holes.....the viewing area on the interior surface kiln wall is only about 3/8" dia. (very small)with tapered plugs that are about 1 1/4" on the exterior surface. The old L&L kiln has 1" dia straight peepholes and is very easy to look in. On the initial test fire of the Paragon with the witness cones in place, you cannot see them through the small hole. Is there any problem in enlarging these holes for better viewing on the interior. The plugs will still seal the holes at the exterior. Maybe this is a question I should ask Paragon before I do it, as I don't want to screw up any warranty with them.

 

One more question...If I add more glaze over what is there, do I need to put anything over it(existing glaze) first..kind of like a primer or bonding agent,for lack of a better term?

 

Thanks again

 

Craig

[Tom]

Ya, ask Paragon about the Kiln before drilling larger holes. No you don,t need a "primer" before add a wet glaze over the firished glaze you might want to heat the piece with a heat gun, hair dryer to help the wet glaze stick. take care not to over glaze it

 

 

 

 

[Peggy1]

I found out that if you set the computer to fire at a cone 6 it actually fired to a 7 in my L&L kiln. So I now set it to a 5(for cone 6 glazes) with a 15 min hold and it works just fine. The 7 witness cone never bends, the 6 is just right and 5 all the way down. Good luck.

[azjoe]

One more question...If I add more glaze over what is there, do I need to put anything over it(existing glaze) first..kind of like a primer or bonding agent,for lack of a better term?

 

 

One trick to help glaze adhere to already-fired glaze is to spray the piece with a light coat of ordinary hairspray... no need for anything fancy, get the inexpensive stuff you can buy at the dollar store. It's basically lacquer. The aerosol can works better than the hand pump because the droplet size is finer. Anyway, it provides enough "texture" for the glaze to adhere to until it's fired (the hairspray burns off during firing). I've also read that spray starch used for ironing works too, but I've never tried that since in my house nothing gets ironed.

[Dinah]

Oh my, do I hear you on this issue. We've all had these heartbreaks. I always use witness cones in various levels of the kiln. I always make a note of start times and finish times, temperature outside, general weather conditions in my Kiln Journal. Make a kiln map and diagram of placement of glazed ware (and any special dip counts or different glaze blends -- you will never recall the names of the glazes when you inspect the ware post firing! ) in your Studio Journal. Helps in long range diagnostics of element wear and so forth, and glaze results. My Skutt 1027 fires about a cone higher. What a shock it was to discover this a few years ago when it was my new kiln. I've also learned to use the ConeFire option to good advantage when I just want a steady firing with no hold on the down fire. Pinnell's Weathered Bronze glaze is a little bit tricksy and I blend it with other glazes in the Bailey Roy/Hessleberth ^6 repertoire to good advantage. RR and JH have also posted an alternative firing schedule to the one in M^6G. Well, JH has and it's worth having a look at it on his website, but as you're no doubt aware of at this point your firing practice will take a couple of kiln loads to figure out. I'm saying this final bit of advice to others, mainly, because you've had a hard lesson: test those glazes before you commit them to your ware. Not in a small test kiln but tests on various bodies, thickness, and blends, dedicated to a proper firing in the normal kiln. You didn't say to what temp/cone you bisque. Anyhoo, it's all exciting and food for thought when the sheep won't jump over the stiles. I've installed a Skutt Envirovent this summer and it's a miracle. Really helps me with firing cycles and schedules.