Glaze Separates From Edges Of Pots When Fired

[Heather O]

Hi there,

I have several glazes that I have to mix up quite thickly to get any depth of colour, however when I fire them they 'pull away' from the edges of the pot leaving a sort of puddled effect. the glaze sort of separates out and leaves gaps where the surface is no longer covered in glaze. This happens even with a thick covering. Could it be to do with the temperature/length of firing? I'm using stoneware clay (oxidising St. Thomas) and various stoneware glazes. I'm firing to 12:30. and using glazes that are supposed to go up to 12:50.

Heather O.

[alabama]

I think it is called "crawling". Sometimes really thick glaze runs and sometimes it separates! I'd thin down the glazes!

 

Alabama

[neilestrick]

Can you post a picture?

[Magnolia Mud Research]

How sharp​ are the edges and how thin is the piece at the edges? 

 

If the edges are sharp and/or  if the work is thin, there will not be enough surface available for the glaze to adhere to the substrate.   The glaze material can detach from the substrate and fall off, leaving behind a bare spot.  If the glaze coating remains intact during the drying the surface tension of the melt can pull the melt back from the edges. 

 

One technique is to round the edges slightly to eliminate the ​sharp​ corners. 

 

LT

[Kaolinwasher]

you may know this but high magnesium glazes may crawl , like mag carbonate, and high feldspar glaze that is thick .also if the bisq pot is dusty , i tree wiping the bisq with a clean sponge .  one thing that helped me is using 1% Vee gum in the glaze  so far i have not had the problem  can you share your glaze formula.  also i tried spraying on glaze and that helped a bit .