phyllos Posted June 8, 2022 Report Share Posted June 8, 2022 Hi everyone! I really need some help, recently I’ve been having issues with my mug bodies cracking while they dry. The clay I use is PF700 and I purchase it from bath potters. I hand build my mugs and cover them up in plastic fully for around 3 days when they are done. After 3 days, I remove part of the plastic so that it can begin to dry slowly and i have had multiple mugs crack in the body, when this has never been an issue before. Is there any advice anyone can give me? Quote Link to comment Share on other sites More sharing options...
phyllos Posted June 8, 2022 Author Report Share Posted June 8, 2022 a picture of the cracks for reference Quote Link to comment Share on other sites More sharing options...
Hulk Posted June 8, 2022 Report Share Posted June 8, 2022 Hi Phyllos! I suppose the good news is the problem appears repeatable. :| How thick are the base portions compared to where the crack is, particularly the corner part? If appreciably thicker/heavier, maybe try a) building so there is more even thickness, and b) place the base on a plaster bat/slab to draw moisture, then set upside down - both to accelerate drying in the base portion. Perhaps other hand builders will have some more/better suggestions; e.g. how to relieve stress when bending the flat slab into a cylinder. Do you wet the slab and coax/stroke it whilst bending? I ease my pulled handles into a curve, which seems to relieve cracking... Quote Link to comment Share on other sites More sharing options...
Dick White Posted June 8, 2022 Report Share Posted June 8, 2022 Are you wedging/kneading the clay when you take it out of the bag to roll the slabs? Clay fresh out of bag will have invisible tension rings in it from the auger of the pugmill. If you slice off a piece and immediately roll it into a slab, those tension rings will still be in that slab and cause cracks as it dries. Wedging/kneading is important for both wheel thrown and handbuilt work. Quote Link to comment Share on other sites More sharing options...
Min Posted June 8, 2022 Report Share Posted June 8, 2022 @phyllos, could you go step by step and describe how you hand build your mugs? How dry the slabs are when you form them, when you are sponging and how wet, if you are partially drying them on a former... anything else you are doing to make them. More info might help narrow down where the problem arises from. Welcome to the forum. Quote Link to comment Share on other sites More sharing options...
Babs Posted June 8, 2022 Report Share Posted June 8, 2022 Are you drying pots on rims? Best to flip as soon as firm enough. Poss damaging pot when applying sprig and handles...wetting pot too much when applying sprig? As Min writes, give us the step by step. Rae Reich 1 Quote Link to comment Share on other sites More sharing options...
oldlady Posted June 9, 2022 Report Share Posted June 9, 2022 add thickness when you reply, please. they look very thick to me and the weight of the sprig and enormous handle does not help. Roberta12 1 Quote Link to comment Share on other sites More sharing options...
Babs Posted June 9, 2022 Report Share Posted June 9, 2022 You say you removwe part of the plastic after 3 days. This would lend itself to uneven drying. Bath, England, summer noe, air hotter and drier , wind across pots? Quote Link to comment Share on other sites More sharing options...
kel-kay Posted June 11, 2022 Report Share Posted June 11, 2022 I noticed the cracks are consistent to either side of the handle, not with hand or its opposite side. So try one new mug, plastic wrap around the top of the mug where cracking begins, flip the mug up side down to allow the bottom to dry more quickly and be sure to support the weight of the handle if there is room between the rim and the top of the handle to so. The weight of the handle could cause additional stressing. Also check with your supplier of the clay to be sure the recipe did not change. I have had the same issue with slip casting on a recipe that failed for glazing, and noticed if I do not put something on top of the mold to where the top dries faster then rest of it, it begins to pressure crack before I know typically when to pull the piece. So seems like the same issue just one is hand thrown/made the other is from casting mold. Quote Link to comment Share on other sites More sharing options...
Hulk Posted June 11, 2022 Report Share Posted June 11, 2022 Aye, good eye kel-kay. Looks also that the slab join lines up with the handle as well, hence the process of bringing around the edges in initial formation of curve to round (from flat slab) puts the extra stress right where those cracks are. Maybe. Quote Link to comment Share on other sites More sharing options...
Babs Posted June 11, 2022 Report Share Posted June 11, 2022 Also seems to be random brush marks on the pots and on the rim. If doing slip work and clay is already too far past optimum dryness the spray the entire pot before adding slip ti try to even out moisture. If you could find/make a chuck to support your mugs when applying handles and sprigs, that would remove accidental pressure on part of pot not beingvworked on. Quote Link to comment Share on other sites More sharing options...
kel-kay Posted June 11, 2022 Report Share Posted June 11, 2022 7 hours ago, Babs said: Also seems to be random brush marks on the pots and on the rim. If doing slip work and clay is already too far past optimum dryness the spray the entire pot before adding slip ti try to even out moisture. If you could find/make a chuck to support your mugs when applying handles and sprigs, that would remove accidental pressure on part of pot not beingvworked on. That could be too, when she handles the mug, it might be where its cracking since she has to apply some pressure to hold it in place while she does the add ons. It causes a hair line crack not visible to the eye and when it dries it opens up. Another idea for having the mug dry evenly is flip on its top then put a big enough container over the mug to help prevent air flow. It obviously will take longer for a dry time but the less you handle it the less possible for hair line cracking. Quote Link to comment Share on other sites More sharing options...
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