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Hardening On Underglaze


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I find that if I use underglaze on bisque and then clear glaze over the top, it does not always go so well.  If I have a bisque firing with room, I just pop the item back in to re-bisque and all is well. However , does anyone know what is the lowest temperature that will harden on the underglaze, for when I do not have a current bisque fire to pop the item back into ? I have had pretty good luck with 450 degrees F. in my regular home oven, but would love to hear other's experience with this

Thanks

Val

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Are you dipping or brushing the clear glaze?

 

In my studio we prefer to put the underglaze on bisqueware because it dries quickly and we don't have to worry about breaking greenware. We don't have any problems with the clear glaze going on (dipping) as long as we let the underglaze dry overnight. If the underglaze hasn't dried completely, it won't take glaze very well.

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why are you not using the underglaze on greenware?  that way the bisque firing sets it.

 

 

Yep, that's what I do, and STRONGLY suggest my students do as well.  I have found, that if you underglaze, then clear for the same firing, the underglaze can be smeared.  The moisture in the clear can soften the underglazes causing them to smear.  If you're careful, it's not an issue, but using the underglaze before, removes this issue all together.  

 

Also, using underglaze on greenware, allows you to touch up any spots, for the glaze firing as well.

 

I should point out, that I brush the clear on.  I imagine dipping, like Neil mentioned, won't cause the issues with the underglaze, that brushing can.

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I am dipping and brushing, but it's mostly where I leave white unpainted bisque that I see differences in how the glaze absorbs ......thicker in the white areas even when drying overnight.

 

As to the why: Several reasons: we make a lot of beads and if you dump all the under glazed beads together to bisque, the colors rub off on each other. Even when we separate by color, sometimes chunks of underglaze stick to their neighbor bead leaving the clay showing on one bead and a lump on the other.

 

Another reason is that I am sometimes afraid I will break the greenware, or I have spent too much time on the greenware, and if something goes wrong at the painting stage I can wash everything off and start over. Often I do underglaze the greenware, but other times it's just not the best solution for me and my work.

https://www.pinterest.com/valgarber/my-art-work/

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Val ...

Multiple firings of underglaze decorated pieces is not uncommon for the exact reason you state ... Too much time and effort goes into the piece to take any risk with smearing ...I have heard of some pieces being fired a dozen times before they are glazed ... so go ahead and experiment with various temps for the in between firings.

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I also prefer applying underglaze to bisque.  Helping to avoid smearing is one reason.  Another is, some underglazes are more refractory than others and, when applied on bisque and then a clear put over them, will show through the clear.  Another, glaze compaction.  The clear over the underglaze compacts it as it forms its bond with the clay body.  Having fired the underglaze first at bisque, you get better compacting (smoothness) when you glaze fire. 

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I think it's interesting the way we all have different methods of using underglaze. I start painting it on at the soft leather hard stage all the way up to bone dry depending on the look I am going for. Then I bisque at 04 and will sometimes continue to add design to a piece with underglaze at this stage. Sometimes I fire at bisque again sometimes I just glaze and fire.

 

On soft leatherhard up to leatherhard I can get really nice watercolor type washes, bone dry gives me very sharp lines and clean up is easy if I make a mistake. I can also carve into the designs doing it this way. After bisquing I will add details I want separated clearly from the colors around it like highlights and contrast. I almost always rebisque if I do a lot of black or dark blue as I have found those colors are really touchy about have a glaze put over them without setting the underglaze. They will have color shifts or even run into the clear on top of it.

 

T

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Do you mean it looks streaky with darker and lighter areas? Or it runs in streaks from the glaze you put over it?

 

My suggestions are:

1) Paint it on leather hard I always get better results with large flat areas doing it at this stage, the underglaze seems to melt together more evenly.

2) When you brush it on at any stage paint each layer at 90degree angles. Meaning paint layer 1 up and down let it dry then paint layer 2 left to right. I find 2 layers is usually sufficient but some colors are more finicky about it than others if so the third layer is needed do it diagonally from bottom left to upper right or vice versus. What you want to do is give the surface it's best chance at having an even coat applied and if you brush all the layers on in the same direction you are more likely to have streaks appear.

3) if you are doing a large area of all the same color dampen the surface before you paint on the underglaze as this will help disperse the pigments in a more equal pattern and will help your brush strokes disappear as well. This of course does not work if you are doing patterns and details as they would become blurry.

 

I hope this helps.

 

T

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