Cenknst Posted March 25, 2020 Report Share Posted March 25, 2020 Hello everyone, I've been working on this piece and had the first two samples that worked out beautifully. However, after the first two, each attempt ended up having this annoying crack (while in the drying process) and couldn't be repaired with slips or vinegar or anything. I'm making them through hand-building. The size is 20x10x6cm. I lay the top slab after I cut out the whole, wait a little for it to get a bit dryer so that it won't be sagging downwards. I'm using the regular vacuumed clays that are ready to use. I'd appreciate if you could advise anything that may help. Thanks in advance, Cenk Link to comment Share on other sites More sharing options...
Hulk Posted March 25, 2020 Report Share Posted March 25, 2020 Hi Cenk! You might try slowing the drying process - so the piece can dry more evenly; once you've finished joining the seams, burnishing, etc., invert a container (looks like a half gallon pail would be big enough) over it. Mist the piece lightly with a spray bottle (water), and shoot a little cloud of mist in the bucket before enclosing the piece. I cover pieces to control drying, mostly until I get around to trimming and finishing, but also to avoid cracking handles. One of the clays I'm trying is inclined to crack handles... I abhor plastic film for controlling drying, as the weight of hanging plastic can deform pieces, it can stick and leave marks, and any clay on the plastic dries out and goes airborne - yuck alla way 'round, imo, hence assortment of containers for enclosing in progress work! Where the container rim is flush against the counter, work dampness can be maintained indefinitely, given periodic misting (watch for mold). Although a "damp box" could be very handy, just haven't got around t'that, and I can only work on one thing at a time... Link to comment Share on other sites More sharing options...
Min Posted March 25, 2020 Report Share Posted March 25, 2020 7 hours ago, Cenknst said: I lay the top slab after I cut out the whole, wait a little for it to get a bit dryer so that it won't be sagging downwards. Could also be that the slab is too dry when you bend it into shape. I'ld try cutting the hole out then letting the slab stiffen up while it's draped over a support then joining the pieces. (could use one of the dry pieces as the support with a piece of newsprint between the form and the slab, it will dry quickly this way) Avoid flexing the piece once it's started to get more than soft leatherhard. Cover the edges of the slab where the clay is narrower if necessary so those areas don't dry out more than the rest of the slab. Link to comment Share on other sites More sharing options...
oldlady Posted March 25, 2020 Report Share Posted March 25, 2020 what are you using to produce the hole? how big is it? pressing a tube shape into the clay to make the hole is probably better than using a knife or any other cutting tool. look around for something that size and cut it to make an angled piercing tube shape. Link to comment Share on other sites More sharing options...
neilestrick Posted March 25, 2020 Report Share Posted March 25, 2020 Your slabs need to be at the same moisture level when you join them, or they'll shrink at different rates and crack. Link to comment Share on other sites More sharing options...
JohnnyK Posted March 25, 2020 Report Share Posted March 25, 2020 I would cut the hole after everything is assembled. This way there is no undue stress on the piece. You can cut the hole while the clay still has some moisture in it but before it goes bone dry. Link to comment Share on other sites More sharing options...
Bill Kielb Posted March 25, 2020 Report Share Posted March 25, 2020 11 hours ago, Cenknst said: Hello everyone, I've been working on this piece and had the first two samples that worked out beautifully. However, after the first two, each attempt ended up having this annoying crack (while in the drying process) and couldn't be repaired with slips or vinegar or anything. I'm making them through hand-building. The size is 20x10x6cm. I lay the top slab after I cut out the whole, wait a little for it to get a bit dryer so that it won't be sagging downwards. I'm using the regular vacuumed clays that are ready to use. I'd appreciate if you could advise anything that may help. Thanks in advance, Cenk All the stuff above are great! If you are really stuck, holes cut like this always induce additional stress in the material. This is true no matter the material. When process does not allow the simple fixes often folks will thicken the slab around the hole so it can handle construction stresses without cracking. This is a last resort in my opinion but I did know an artist that would cutout a small slab and punch the same hole through and make himself little washers if you will to thicken the area. He would immediately attach these and go on his merry way with his normal construction, sequence, assembly and drying. Link to comment Share on other sites More sharing options...
Babs Posted March 25, 2020 Report Share Posted March 25, 2020 Would reinserting the cutout until pot totlaay dry help? Just asking Link to comment Share on other sites More sharing options...
Cenknst Posted March 26, 2020 Author Report Share Posted March 26, 2020 Thank you everyone for the tips! I was guessing one of these could be the problem but I wasn't sure as I'm not that experienced. So it seems I'll have to watch out for all these points. Out of the hand-built pieces, I'm only having problem with this one - and this is the only curved one with a hole. On the other hand, I was also assembling the top piece the latest (and with a hole made with a tube cutter) as I was afraid of the mid part sagging. So I'll see what happens when I combine them altogether first, at the same moisture and cut the hole the latest. Maybe I should go for a smaller hole too.. Have a good day and stay safe! Link to comment Share on other sites More sharing options...
CactusPots Posted March 28, 2020 Report Share Posted March 28, 2020 On 3/25/2020 at 10:50 AM, neilestrick said: Your slabs need to be at the same moisture level when you join them, or they'll shrink at different rates and crack. You can assemble hand built forms from pieces of different moisture levels if the first step after construction is not drying but equalizing the moisture across the piece. Every pot I do that has any joinery involved gets a few days in a plastic garbage bag. Once the piece is equal moisture, then it can be dried. I prefer the initial drying to be done between bath towels. Again, even is the key Link to comment Share on other sites More sharing options...
neilestrick Posted March 28, 2020 Report Share Posted March 28, 2020 32 minutes ago, CactusPots said: You can assemble hand built forms from pieces of different moisture levels if the first step after construction is not drying but equalizing the moisture across the piece. Every pot I do that has any joinery involved gets a few days in a plastic garbage bag. Once the piece is equal moisture, then it can be dried. I prefer the initial drying to be done between bath towels. Again, even is the key To some degree, yes. It also depends a great deal on how forgiving your clay body is, and if you have the time and space to leave assembled things covered for days. Covering for a few days is definitely beneficial, but it won't overcome poor construction techniques. Starting with slabs of equal moisture will do more to prevent problems. It would be better to wrap the slabs up together for a few days before assembly so they can equalize before you ever build with them. Link to comment Share on other sites More sharing options...
Pres Posted March 28, 2020 Report Share Posted March 28, 2020 Similar type of form years ago, I followed the process of John Glick. He made a wooden form, with a hinge and screen door latch. This allowed him to place a cheese hard slab into the form, put a top and bottom on the piece while they were also cheese to leather hard. Often he would put stuffing inside, to doam the top of the piece, and then cut off the lid section to remove the stuffing. However, if you timed everything right you could construct it with not stuffing. If the piece collapses a little, then just insert a straw into the area where you will later cut the opening, and blow lightly to inflate the walls back to straight. Just another option in MHO. best of luck, Pres Link to comment Share on other sites More sharing options...
Sorcery Posted April 1, 2020 Report Share Posted April 1, 2020 Can't see the pictures! What changed from the first 2? Could be the furnace is off now and the pieces are drying different? I have radiators, not forced air, if I cover a piece it cracks. If I leave it out it doesn't. Clay, humidity...many factors are important, but your answer lies only in what changed from the first 2! Sorce Link to comment Share on other sites More sharing options...
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