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If you've read our guides on mugs and handles and put our advice to good use then you probably have some successes and some problems, which is why we have these tips and tricks to help you. If your handles (or spouts or other attachments) are cracking at the attachment points before you bisque fire them then they can be fixed, if they crack after bisque then they can probably be covered up, but if they crack in the glaze fire then your best bet is to do everything you can when making them to keep them from cracking.
The best way to make a perfect handle is to take your time and follow all the steps. Step one is to make sure that the handle and cup are ready to be joined. Ideally they should be a soft leather hard - you should be able to handle them both without deforming or leaving finger prints or smudges. Next, score the cup and the handle liberally. Use your needle tool to make deep scratches in multiple directions and apply a generous coating of slip to each.
If you are worried that it might crack then squeeze a little lump of clay into the top of both connection points and smooth it out. It will fill in the places most likely to crack and give a little extra strength.
Finally, let it dry as slowly as possible. Cover it overnight with plastic then paint the attachments with wax resist. Avoid using a fan or any kind of fast-drying.
Sometimes you might have to rush and dry your mugs fast, or your cup and handle may not have been the same dryness and are separating. Sometimes you did everything right and you still start to see a little crack on your handle attachments.
If it's only a small crack you may be able to burnish it out by rubbing it with the back of a spoon, or rehydrate the mug by spraying it with water and re-wrapping it then smoothing the crack out with your finger. If it's a big crack, or the handle is separating from the pot then more drastic action may be needed, but the mug can absolutely be saved.
First use a fettling knife to remove the handle as cleanly as possible. If you are careful then it should come off in one piece (if not, you will need to make a new handle). Spray the pieces with water and wrap them in wet paper towels, or newspaper, and then wrap them with plastic; repeat as necessary until they are leather hard. Score and slip them again and reattach them. But if it didn't work once, what would make it work under these less than ideal circumstances? Try some helpers:
If you find a crack in your handles (or anywhere else in a bisqued piece) you don't have many options, but you can definitely try to cover it up. If it's a small crack then you just dip your finger in clear glaze, drip it into the crack and wipe away the excess with a sponge. Nine times out of ten the crack is only on the surface and the attachment is still strong. If you need to make sure, pick the mug up by its handle.
If the crack is big or the handle falls off when you pick it up then your options are much more limited. Paper clay might stick it back together, but it's not likely. Every potter will say that they know a guy who had a teacher in college who could glaze a handle back on if it fell off. What they really mean is that the teacher used glaze to stick the handle on, and then did some sort of kiln-Tetris to keep it in place while it fired and then somehow it came out looking perfect. To be honest, I have never seen anyone pull it off. What really happens is that the handle falls off again and ruins a kiln shelf.
Cracks and other flaws can be an annoyance, but are often inevitable. Taking the time to learn to fix them is just as important is taking the time to make things right the first time around.
Remember that cracks are rarely random, and will often happen to whole batches of pots, not just one or two, which is why it's especially important to know how to fix them. If you come into your studio to find two dozen cracked greenware handles then it is preferable to take an hour to repair a half-day's labor than to waste another half-day remaking them all.