Jasmineceramics Posted August 9, 2018 Report Share Posted August 9, 2018 I’m just getting started with Ceramics and every time I use a gloss glaze it has these tiny hairline cracks across it’s surface, they actually look quite nice, however, I made a mug the other week and having glaze fired it (with a lead free dinnerware safe glaze) I used it for a cup of tea and there was this kind of hissing/popping sound of air escaping and when I picked the mug up the water water starting to seep through the base of the mug... how do I avoid these tiny cracks so that I can make a watertight mug?? Thank you Link to comment Share on other sites More sharing options...
Babs Posted August 9, 2018 Report Share Posted August 9, 2018 What cone are you firing to? What is the recommended cone to fire your clay body? Sounds like your clay is underscored. That's the starting point imo Then you can work on the glaze fit Link to comment Share on other sites More sharing options...
curt Posted August 9, 2018 Report Share Posted August 9, 2018 The hairline cracks are almost certainly what is called crazing. Do a search of these forums and you will find it is widely discussed. Can you post a photo? the leaky cup may be due to various causes. As Babs is saying we need to know more detail of your clay body and firing to make suggestions. Link to comment Share on other sites More sharing options...
Jasmineceramics Posted August 10, 2018 Author Report Share Posted August 10, 2018 It’s Earthenware- I bisque fire to 1100c so cone 03 and then gloss fire to cone 04. Which is what it says to do on the glaze pot (it’s a spectrum low fire glaze the cracks are tiny! My phone can’t focus on them but I used a macro lens which is x15 (mum just got a phone lens kit which is useful for this) So this photo is by the rim- the mug has a ‘dessert’ glaze on it and then a clear gloss on top- I’d originally just done the dessert glaze but that wasn’t watertight so I then refired with the gloss on top which now has these cracks Link to comment Share on other sites More sharing options...
Jasmineceramics Posted August 10, 2018 Author Report Share Posted August 10, 2018 The mug itself is completely sealed and doesn’t have any cracks or gaps, it’s purely due to the glaze cracking and therefore allowing the water to seep through the porous ceramic Link to comment Share on other sites More sharing options...
curt Posted August 11, 2018 Report Share Posted August 11, 2018 Yep that is crazing. A very normal problem. Your glaze is shrinking more than your pot does as it cools, that is what is making the cracks. A double layer of glaze may be providing too much flux, so I would try getting a thinner glaze layer first and that MIGHT fix the problem. If that doesn’t do it, then get a new glaze, or reformulate the one you have to contain less fluxing power. Not much you can do with the claybody I think, as earthenware is earthenware... Link to comment Share on other sites More sharing options...
preeta Posted August 12, 2018 Report Share Posted August 12, 2018 Jasmine is your claybody meant for cone 03 or higher? Just because you can’t see cracks does not mean they are not present in bisqueware. Glaze is surface. Not through claybody. If you flick your finger nail on bisqueware and hear a thud instead of a sharp tink sound you already have an unseen crack! Use it as glaze test Id say make some food colouring. Bright dark colour. Then dip your crazed cup in it and then take it out and wipe off. Or brush on and wipe off. Or India ink. You will be able to see where the water goes through crazing. If you refire to even 04 the colours should burn off. Link to comment Share on other sites More sharing options...
Rae Reich Posted August 12, 2018 Report Share Posted August 12, 2018 14 hours ago, preeta said: Jasmine is your claybody meant for cone 03 or higher? Just because you can’t see cracks does not mean they are not present in bisqueware. Glaze is surface. Not through claybody. If you flick your finger nail on bisqueware and hear a thud instead of a sharp tink sound you already have an unseen crack! Use it as glaze test Id say make some food colouring. Bright dark colour. Then dip your crazed cup in it and then take it out and wipe off. Or brush on and wipe off. Or India ink. You will be able to see where the water goes through crazing. If you refire to even 04 the colours should burn off. Or you can use hibiscus tea (learned inadvertently). Link to comment Share on other sites More sharing options...
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