PDA

View Full Version : My mugs cracked overnight



Hairy Potter
01-03-2010, 07:02 PM
Hi,

I have been trying to hand-build mugs using stoneware clay that I got about 10 months ago. I am not sure why... but I have made 6 mugs up till now and every single one have cracked after I left them dry overnight.

I have tried putting them in a cold room and a room with heat on but neither of them worked. They all split at the joints.

Can anyone suggest what the problem/ solution is?

Thanks in advance.

Hairy Potter Sniff Sniff

C Hupfield Ceramics
01-03-2010, 07:53 PM
Hi,

It might be that you are leaving them to dry out too quickly. Some clays especially stoneware needs to dry in stages. Try leaving the mugs out in a cool room for an hour or so after you have finished working on them, then wrap loosely in plastic or a carrier bag. This will still allow the clay to dry but not as quickly as it would out in the open air. Then take the plastic off the next day and leave for a few hours. Repeat this until completely dried out. Introducing the clay to gradual spurts of air will ease it to dry out in its own time.

I wouldn't expect them to be dry over night. Even if you don't find any cracks when the clay is completely dried out, you might notice some cracks at later stages during the stoneware firing because the clay was dried too quickly.

I wouldn't recommend drying the mugs in a heated room as the heat will be forcing them to dry, stressing the clay, causing cracks.

Alternatively it might be that the joints on the mugs aren't strong enough. How are you joining them?

Hairy Potter
02-03-2010, 06:36 PM
Thanks for the advice! You are absolutely right. I used to cover them with plastic bags and since it's been a while I haven't done any work I forgot!

How I joined them... I first scored the joints and then apply some self-made slips (made with the clay, water and a few drops of vinegar). I wonder if I should add vinegar in the slips.

toppotter
02-03-2010, 09:35 PM
yes slow drying is the key, if there is too much water in your slip you stand more chance of getting cracks.

you might try this technique. take a tooth brush or better a suede brush with metal bristle. Wet it and score the areas you want to join. you will produce the slip you require to join when you score.

any pics of your mugs?

regards

C Hupfield Ceramics
02-03-2010, 09:47 PM
I've never used vinegar in slip, I always use just clay & water to a paste consistency - not runny. Could the vinegar be causing the joins to crack?

Chicita
03-03-2010, 04:37 PM
I've used white vinegar neat to join unfired pieces that are already dry, such as a mug handle that has fallen off. A bit hit and miss really as I've had successes and failures with this one but it's supposed to work.

Hairy Potter
10-03-2010, 08:02 PM
yes slow drying is the key, if there is too much water in your slip you stand more chance of getting cracks.

you might try this technique. take a tooth brush or better a suede brush with metal bristle. Wet it and score the areas you want to join. you will produce the slip you require to join when you score.

any pics of your mugs?

regards

I think part of the problem that the slip is a bit too runny. I would try using the brush. I took a picture but I can't upload it as the file size is too big. I will try again later. Thanks, toppotter.

Hairy Potter
10-03-2010, 08:06 PM
I've used white vinegar neat to join unfired pieces that are already dry, such as a mug handle that has fallen off. A bit hit and miss really as I've had successes and failures with this one but it's supposed to work.

I think vinegar is supposed to work. I got the idea from an online video. Thanks, Chicita.