How can I stop surface cracks around my joints during drying? (I feel like I’ve tried everything)

[carlymakesmugs]

Hi pottery experts,

I hope this message finds you well, I really appreciate all the incredible advice you share.

Here’s my dilemma: of the recent 60 mugs I made, only 2 survived to bisque without cracks near my joints. This is a relatively new issue I’m experiencing, I made over 100 mugs last year without this happening. I’ve been trouble shooting a ton and I can’t sort out what else I should try. (Here are pictures of the cracks: https://imgur.com/a/uNN7saX

My current process:

Day 1

• throw my pots
• flip them over as soon as they are dry enough to handle
• trim them
• make my handles (I extrude and shape them)
• store the bodies and handles in a sealed container overnight, and spray them more for good measure

note: I pay special attention to keep everything on the wetter side of leather hard

Day 2

• attach my handles
  • I score both the handle and mug body (I score an area much larger than is needed for the attachment)
  • I add a magic clay mixture I make out of the dried trimmings from that clay, vinegar, and toilet paper pulp
  • I press them together tightly, and then give it a minute or two to set
  • I use a roll of clay to blend between the handle and body to create a smooth transition - the clay I use for this is slightly softer because that blends so much more easily - I suspect this is where some of my problems are coming from I always thought that leaving the mug’s moisture to equalize the first few days might be avoiding having issues from this
• store them in the sealed container again

Day 3

• touch up the mug and attachment with a lightly wet sponge to get everything smooth
• (sometimes) cover the attachment area with wax resist - I haven’t found this to help so I’ve stopped

The next 16-30 days

• I let them slowly dry in the closed container (I used to just wait a week, but I’ve slowly tried waiting longer and longer)
• As they get more dry I started to take the lid of for the daytime, and close it again at night
• Once they’re close to being bone dry I leave them uncovered for another week
• I’ve tried repairing these cracks at the greenware stage by scoring and then layering on my magic clay mixture, or rubbing the crack away before I bisque fire - but the cracks always re-emerge.
• Sometimes that cracks aren’t visible in the greenware, but when I submerge them under water after they’ve been bisqued they bubble revealing small fractures.

 

Additional notes:

• I started having this issue when the formulation of the clay I use changed. I’ve been using PSH 516 (from pottery supply house), they changed their formulation last year due to supply chain shortages. But since then I did a test with an older batch of clay I had around and the cracks persisted, so I’m suspecting it’s not just the clay. I even tried it with a reliable grogged clay I use and had the issue still.
• I’d prefer not to change the shape of my handles if possible, I really love the look of them and they way they blend into the body - but I do understand that it creates a slightly thicker section in my pot.
• I have been throwing with my clay on the softer side, because I was experiencing carpel tunnel symptoms. I’d prefer to keep working with the clay while it’s softer because it’s so much easier on my wrists.
• I also recently moved from Ontario to Montreal, and in my new workspace there is much more humidity.
• I recently tried PSH 910 (a popular porcelain), I kept my process the same, but I dried the mugs much faster within a week of throwing them. I tested this with two mugs, 1 survived without cracks, but one had the same cracks. Maybe using this new clay but keeping my longer drying period would help?

 

My questions:

• Are there alternative clays you’d recommend? In my area I have access to Laguna, Plainsman, Pottery Supply House, and Tuckers. Are there certain properties I should be looking for in a new clay? (i.e. less shrinkage, less absorption)

• Would you recommend I change my process in any way? I’m open to trying anything.

 

Thank you for your time and for sharing your knowledge. I’d appreciate any recommendations you have.

Carly

[Callie Beller Diesel]

Hi and welcome!

I would venture that if you’re getting the same cracking in different climates and with different clay bodies/batches, it’s not the material. 

I think your observation about the join being too thick is a possibility, but I’d have to see the thickness difference to confirm.

What I think is more likely is that you’re adding water back into the pot at the wrong times, possibly at multiple points from your description, and that’s causing a little readsorbtion, which is what happens when clay starts to reclaim. The good news is, the solution involves working less than you are.

-Start by not sponging. Sponging pots for cleanup is make-work. If you aim to handle pots at the stage where you’re not leaving fingerprints and keep your hands clean so you’re not adding crumbs, you eliminate the need to sponge and save yourself a bunch of time that you could use to do something much more fun.

-Damp box use: If you need to increase the humidity inside your damp box you can put a damp sponge in next to but not touching them, or add a little water to the plaster (if you’re using plaster). Don’t spray the pots. Another possibility is that if your damp box is getting condensation that drips back down onto the pots, that’s reapplying water in your absence, causing that readsorbtion. You also might try opening the damp box gradually over a period of 3-4 days rather than doing a fully covered/no covered method. Think even circulation and drying, not slow. Slow done wrong doesn’t mean even. I think drying mugs that need no further work for 30 days is unnecessary.

-When you’re doing the handle attaching, rather than adding a coil, beef up the cut end of the handle by tapping it so that it flares a bit. This will leave extra clay for smoothing and increase the surface area of the join itself, making it stronger. It’s my opinion that magic water shouldn’t be necessary in most mugs, but if you do choose to use it, use it sparingly to make a small amount of slip on the site as you score. Regular water works this way too.  

-Remember to wiggle!  If you push and wiggle until it stops sliding around, the handle may break on either side of the join, but the handle won’t separate from the body. If you’re generously applying vinegar slip, again you’re adding water. When you remove the ooze from the edges of the attachment points, think about wiping the piece dry, not cleaning it up like you’re wiping a countertop. Remove extra moisture/slip with a well wrung out sponge or a clean, damp watercolour paintbrush.

Things I think you’re doing right:

I don’t think you need to use stiffer clay to start with: save your wrists.

Drying pots upside down! If you’ve got a thicker attachment point on the outside of the pot, trapping humidity inside the thinner walled mug body slows down the drying of the thinner bits, and gives the handle a chance to catch up.

Everything you’re doing on day one. 10/10, no notes.  

[carlymakesmugs]

48 minutes ago, Callie Beller Diesel said:

Hi and welcome!

I would venture that if you’re getting the same cracking in different climates and with different clay bodies/batches, it’s not the material. 

I think your observation about the join being too thick is a possibility, but I’d have to see the thickness difference to confirm.

What I think is more likely is that you’re adding water back into the pot at the wrong times, possibly at multiple points from your description, and that’s causing a little readsorbtion, which is what happens when clay starts to reclaim. The good news is, the solution involves working less than you are.

-Start by not sponging. Sponging pots for cleanup is make-work. If you aim to handle pots at the stage where you’re not leaving fingerprints and keep your hands clean so you’re not adding crumbs, you eliminate the need to sponge and save yourself a bunch of time that you could use to do something much more fun.

-Damp box use: If you need to increase the humidity inside your damp box you can put a damp sponge in next to but not touching them, or add a little water to the plaster (if you’re using plaster). Don’t spray the pots. Another possibility is that if your damp box is getting condensation that drips back down onto the pots, that’s reapplying water in your absence, causing that readsorbtion. You also might try opening the damp box gradually over a period of 3-4 days rather than doing a fully covered/no covered method. Think even circulation and drying, not slow. Slow done wrong doesn’t mean even. I think drying mugs that need no further work for 30 days is unnecessary.

-When you’re doing the handle attaching, rather than adding a coil, beef up the cut end of the handle by tapping it so that it flares a bit. This will leave extra clay for smoothing and increase the surface area of the join itself, making it stronger. It’s my opinion that magic water shouldn’t be necessary in most mugs, but if you do choose to use it, use it sparingly to make a small amount of slip on the site as you score. Regular water works this way too.  

-Remember to wiggle!  If you push and wiggle until it stops sliding around, the handle may break on either side of the join, but the handle won’t separate from the body. If you’re generously applying vinegar slip, again you’re adding water. When you remove the ooze from the edges of the attachment points, think about wiping the piece dry, not cleaning it up like you’re wiping a countertop. Remove extra moisture/slip with a well wrung out sponge or a clean, damp watercolour paintbrush.

Things I think you’re doing right:

I don’t think you need to use stiffer clay to start with: save your wrists.

Drying pots upside down! If you’ve got a thicker attachment point on the outside of the pot, trapping humidity inside the thinner walled mug body slows down the drying of the thinner bits, and gives the handle a chance to catch up.

Everything you’re doing on day one. 10/10, no notes.  

Thank you so much Callie! ❤️ This is so so helpful. I have definitely been reintroducing a ton of water in that first week, I’ve been spraying my pots so much. I’ll going to try throwing another batch on Monday, and make sure not to introduce any new water once it’s been thrown. I’m excited to try beefing up the cut end of my handle too, that sounds like it’ll be much more efficient than adding and smoothing the coil. Thanks so much for taking the time to reply,  I’ll let you know how this next batch goes! 😊

[Babs]

I think this has been discussed before. I had a similar prob and it is the shrinkage and moisture difference thingie  @neilestrick advised on it which worked for me.

I ended up making handles, covering tthem with plastic, trimming pots at quite a soft leatherhard and attaching straight after, water with a bit of vinegar, or throwing water  scratched onto mug with a tooth brush works for me. I sometimes spray handles with water if I have been a but slow and day hot.  Handle end smishwd and scratched with tbrush. Squiggle handle onto cup scratthed area, add any coil at this point, smooth aka Callie and leave to dry how you normally dry.

Neil wrote re softer pot, harder handle helped cope with the shrinkage problems, I Think! Worked for me.

Hope he confirms..But if handle tooo dry it may crack in firing...