Sculpture lesson: Cracks

As a sculptor in clay it is very disappointing to fire art and have it come out of the kiln either broken or cracked. More often than not handbuilt clay art work has cracks – it is the nature of the beast. In order to ‘save’ your work there are important techniques that anyone working in clay can apply to any artwork and have a better chance at success.

Here are the steps :

1.  When sculpting the piece ensure the soft clay is joined correctly. Here is a video by ceramic arts daily to demonstrate proper handbuilding techniques

2. Make certain your piece is dried completely prior to firing the piece. Know your clay and the appropriate firing temperatures before attempting to fire your work. Firing too high or too low will not give you the results that you want. I once worked for weeks on a figure that I blew up in the kiln because I had changed my clay and fired it too high. A regret and lesson to double check the instructions on the box. Dry your piece slowly —no need to rush. Work on other projects if you are itching to get it in the kiln – distract yourself if necessary.

3. After your work is dried completely fire in the kiln at a low temperature. I fire my art to a cone 018. I fire on the lowest setting for 2 hours than bring it up slowly over a 6-8hour period. Once it has been fired I leave it closed and let it cool down completely and overnight before I open the kiln.

4. Remove the work from the kiln and check for apparent cracks or broken pieces. Submerge the bisque fired clay into a bucket of water and check for small or hairline cracks. Cracks are often not even noticed at first but will become evident once the bisque is wet.

5. Mix together with a handheld blender/mixer vinegar and toilet paper until the consistency of baby pablum, add dried powder clay (same as the clay used for the project) and mix and blend together with the vinegar pulp mixture until a smooth paste. Fill cracks and repair broken pieces with the mixture. do not worry too much about bumps as they can be sanded later after the piece has dried, lightly and carefully sand with a q-tip. Before continuing make certain the piece is completely dry PRIOR to firing again. At this stage you can either sand,smooth, glaze the piece  and fire to full temperature.

Recipe :
Vinegar, toilet paper, clay ( from your source – dried and pulverized until powdered or no more than 1/4 ” pieces. The acid  in the vinegar will break down the toilet paper and clay particles.

6. Or you may also dry completely and refire to cone 018 – until you are certain there is no more cracking or repairs needed. After it is removed from the kiln resubmerge in water and sand off any bumps from the paperclay. The final phase is to finish with a Glaze application and fire to temperature.

If you have any questions let me know I would be happy to discuss or workout any technical issues you may have Or queries on techniques. I am working on getting photos of this process and will post shortly.