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olpupi

Glazes scratching and soft

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I recently  fired a couple loads of work to c5 with no unusual events. Load had plates with a few comm'l glazes and one I made. Witness cones came out as usual with c5 down and c6 nodding. I've used all of these glazes on plates before with no problem. This time all came out soft... could scratch them with the edge of a spoon. The kiln is outside and outdoor temps overnight were down in the low 20's and kiln finished early morning when temp was high 20's. Ran another load which went overnight but finished mid day with temps in the 60's.  Same results with glazes: easy to scratch and not as smooth as usual... feel kind of sticky when your run your hand over them. Look perfect and shiny as usual.

Any thoughts on what the problem may be? Since it's all the glazes it has to be the firing, but cones down as usual. What the heck? 

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 For the last load that came out soft I had mixed a new batch of one of the commercial glazes using new product sent by producer. Came out with the same problem. So, I usually make only 1-2 gallons of glaze at a time an de use it pretty quickly, so don't think the problem is mixing 

If glazes in buckets froze (not solid, but just on top) would that change something enough to cause this problem? 

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4 hours ago, olpupi said:

... could scratch them with the edge of a spoon.       ...  easy to scratch and not as smooth as usual... feel kind of sticky when your run your hand over them. 


What do you mean by "could scratch with ... a spoon" and "not smooth as usual ... feel kind of sticky"?
 

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A knife or edge of a spoon rubbed against the glaze left a scratch... not a mark... a scratch in the glaze that cannot be removed. 

Normally it feels glassy smooth... with this problem my hand  catches a bit on it. Like it's a little bit sticky... not gooey.... just not smooooooth and glassy, so I imagine there must be some texture there that isn't usual. But the glazes all look fine. 

 

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Sounds like your supplier may have sent you a bad mix of glazes. It sounds like they send you a premixed bag, so I would contact them and see if any of their materials may have changed. It does not sound like a user error on your part, but a problem with the glaze ingredients.

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Douglas... I always hope for the problem not being user error, but the buck stops at the potter more often than not. I'm not leaning toward glaze blame because the problem was the same for comm'l glazes and one I made, and I did another firing with different batch of same comm'l glaze and it happened again. Whole load had the problem x 3 loads.  :-( 

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