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Underglaze On Lidded Pot Lids?


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#1 Ginny C

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Posted 29 September 2013 - 02:33 PM

Will regular underglaze on leather hard clay applied to the rim of the pot and its lid cause them to stick together if fired together in bisque firing?

 

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#2 Pres

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Posted 29 September 2013 - 02:40 PM

I haven't ever had that happen to me before. I usually do not apply underglaze between the two surfaces, but accidents do happen. When ever I have had an accident, I usually wash it off, but sometimes will miss them.  When missed, the lid and pot did not stick together.


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#3 Doulla

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Posted 29 September 2013 - 02:58 PM

I once put a small sculpture that was underglazed onto another underglazed piece and it stuck. This happened during the stoneware firing. It did come apart though with a bit of gentle persuasion but I made sure I didn't repeat it.



#4 Benzine

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Posted 29 September 2013 - 04:35 PM

I've used underglaze on a lid and rim before, with no issues. You just want to make sure the underglaze has dried first, otherwise it would almost be like attaching the two pieces with slip.

I should note that I have mostly tried it on low fire wares. At Cone 5, the underglaze did seem to slightly stick.
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#5 Ginny C

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Posted 29 September 2013 - 04:42 PM

I haven't ever had that happen to me before. I usually do not apply underglaze between the two surfaces, but accidents do happen. When ever I have had an accident, I usually wash it off, but sometimes will miss them.  When missed, the lid and pot did not stick together.

Ah-ha! That's what I hoped, that they do NOT stick together. I haven't done it yet, but I'd like to have some color on the rims and I thought that the matte finish of an underglaze might work well. I don't much like the bare clay look of the white B-Mix 5 I'm using. I'd like to do the same thing on the feet. Not as an accident but on purpose! Perhaps watered down underglaze, just wiped on lightly before the bisque firing?  Then firing the lid on the pot.  What do you think? Will they stick together?

ginny



#6 Pugaboo

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Posted 29 September 2013 - 05:51 PM

I have done several lidded pieces with the rims painted with underglaze. I use Amaco LUG underglazes and Little Loafers stoneware clay. My results have been very little or no sticking with a ^04 bisque firing. There was some color transference though so make sure you do not try 2 different colors the worst seems to be the darker underglazes like black and dark blue. The issues arise with the final glaze firing.

I fire to ^6 in an electric kiln. I use Amaco Zinc free clear or Coyote color glazes. I put no glaze on the rims or feet. I wax the feet and rims with either liquid wax or a liquid wax with a bit of Alumina mixed in it. My results have been that several of the pieces with underglaze rims and/or bottoms stick to each other or the shelf during a cone 6 firing. It's never a whole lot but had one piece pull a tiny junk of a bottom of a bowl off and was very apparent so had to toss the bowl. The other 3 bowls in the set did not stick at all so not sure why that particular bowl did, I checked the shelf and there was no glaze stuck to it from previous firings. On a lidded box I painted the rims with a light blue underglaze, bisque fired perfectly with no sticking, brushed with alumina wax, glazed rest of box making sure I got no glaze on or near rims, glaze fired and box fused together in 2 tiny spots pulling the underglaze off and even a small sliver of clay. I decided to try something since it was a total loss at that point and used a Dremel to smooth each of the rims then reapplied the underglaze. I bisque fired the piece again with lid on box, did not stick, but new underglaze was a slightly lighter tone than the original underglaze. I refired the box in a glaze firing by seperating the lid and the bottom and stilting them both. It worked beautifully new underglaze fired to same color as original, the glaze did not change color dramatically and the box did not warp. The only change was, because of the stilts I now have 3 tiny impressions on the inside of the lid but that I can live with.

I would not stack underglaze decorated items in any firing face to face unless the patterns were identical and the colors also identical. I say this because I have had the darker underglaze colors transfer a slight shadow onto shelves even with just a bisque firing. Glaze firings are even worse even if you don't use any glaze. I really don't care for the white line around the bottoms and edges of some of my pieces so I am trying different things to see how I can minimize that line between decorated or colored clay and the edges or bottoms. I am trying to get educated on colored slips thinking to try that on the bottoms in a complementary color. I'm sure there are other things that I can try as well just kind of working my way through one technique at a time.

I hope this helps and I would be interested to know how your efforts turn out.

Terry
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#7 bciskepottery

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Posted 29 September 2013 - 07:15 PM

Your underglaze will contain a flux -- generally a frit -- to help it melt and adhere to the surface of the clay.  In a few instances, depending on the color, the underglaze frit may cause it to stick to a surface it is touching . . . a lid or even the kiln shelf.  Good news is underglaze does not melt like a glaze and most items that become stuck together can be separated with a few taps and with no damage.  You might need to touch up the spot where they stuck, but that is no big deal.  From my experience working with underglazes, you are more likely to have no problems than to have a problem.  Just make sure the applications are even and not too thick or heavy.  And, make sure you let them dry completely before sitting them on top of each other. 

 

You could also consider adding the underglaze when the items are bone dry or closer to bone dry than leather hard.  The underglaze will absorb faster and be less likely to stick to the surface it is in contact with. 

 

Underglazes on the bottoms work . . . just with the caution that some underglazes may transfer color to the kiln shelf and may, in some instances, stick -- its that flux thing.   On the bottom, you can wax over the underglaze. 

 

Pugaboo . . . Little Loafers has some characteristics of porcelain -- including the tendency to pluck (or fuse itself to the kiln shelf) if fired above maturity.  The alumina in wax is the best way to reduce the chance of that happening. 






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