Jlynch Posted July 2, 2021 Report Share Posted July 2, 2021 Hi! A couple of questions here... I have recently mixed up a batch of a (usually) very reliable glaze, only to find the glaze to crack and pinhole really badly on application to the bisqueware. The only change I have made to the recipe was substituting the usual Custer feldspar (out of stock at my usual supplier) for potash feldspar. This leads me to my first question... I am aware that Custer feldspar is a high potassium feldspar, though it differs from standard potash feldspar? How so? I have read conflicting information concerning this subject. Second question: could this be the reason why the glaze is suddenly cracking/pinholing on application? Or am I barking up the wrong tree?! Perhaps I unwittingly mixed the batch wrong. The recipe is: woll 5.5 cus feld 28.5 epk 28 silica 15 dol 19 gerst b. 4 (plus stain and Epsom salt) I’m terrible at not knowing how a glaze works until it starts going wrong, and this one has been thoroughly good to me for a good few years, until now! Any help would be greatly appreciated. Link to comment Share on other sites More sharing options...
neilestrick Posted July 2, 2021 Report Share Posted July 2, 2021 So the problem was with it cracking when you applied it, not in the firing? There is no 'standard' potash feldspar, just different potash spars from different mines. Do you know which feldspar you used this time? Link to comment Share on other sites More sharing options...
Jlynch Posted July 2, 2021 Author Report Share Posted July 2, 2021 Thanks for clearing that up re potash feldspar. The one I’ve recently bought was sold and labeled as Feldspar Potash, originally mined by Euroarce in Spain by the looks of the bag. The glaze cracks before firing. It can be smoothed over and fires okay but obviously would rather not spend ages smoothing over the cracks before firing. Link to comment Share on other sites More sharing options...
Jlynch Posted July 2, 2021 Author Report Share Posted July 2, 2021 Ah! I think I may have found the culprit! The other day I used the glaze as soon as I had mixed it, cracks/pinholes appearing as the glaze dried. This evening I thought I’d try again and it dried onto the bisqueware absolutely fine. I’ve usually managed to mix and use this glaze straight away, but perhaps with this new feldspar I can no longer get away with it! Link to comment Share on other sites More sharing options...
neilestrick Posted July 2, 2021 Report Share Posted July 2, 2021 Interesting! I guess it just needed more time to fully hydrate. Glad it worked out. Link to comment Share on other sites More sharing options...
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