Monthly Tech-Tip | No tracking! No ads! |
Ordinary laminations from improper pugging can simply be wedged out and the clay is still fine to use. But freezing is a different matter. No chemical changes happen when clay is frozen, the water connections between clay particles are simply disrupted and it becomes a soggy mess. So it might seem that warming it up and wedging it should restore the plasticity - after all it was in the ground for millions of years and was frozen and thawed countless times)! But simple wedging does not work, the reason for that is not entirely clear (since the freezing only disrupts the clay on a physical level). Either repugging or drying it out and rewetting are the only practical ways of making it useable.
These are cross-cuts from slugs of a production run of clay that was improperly pugged (inadequate vacuum). The problem is not often evident at time of extrusion but exhibits after weeks or months of storage. This clay body does not contain significant fine-grained material, but 2% talc is added to aid vitrification. The production crew claims that this talc makes it doubly important to monitor vacuum at all times (or laminations will result). These are not actually a problem if you wedge the clay well. But if you do not (e.g. inserting them into a hand-extruder, pressing them in a mold) then they "build in" failure points that will initiate drying and firing cracks later. Even if pieces survive the drying and firing processes, weaknesses will persist making them more prone to failure-on-impact or stress. This being said, does that mean you do not need to wedge plastic clay bodies if they are not laminated? No. All clays laminate to some extent because clays have such incredible particle surface area, even the best pugmills cannot wet the surfaces of all of them.
Buy me a coffee and we can talk