Many people do not realize that greenware can get old. When it gets old it is more difficult to clean and there is more risk that it will warp or crack during firing. I’ve been in ceramic shops where some of their greenware looks like bisque, it is so old it has become white. From all appearances it seems to be harder and therefore stronger, but it isn’t.
Of course, as it ages, the moisture leaves the ware, so one might think there will be no problems – at least it won’t explode in firing, right? Well, most likely it will not explode, but other problems can arise. I do know that the structure of the clay particles become weakened over long periods of time. Perhaps that is due to the 100% loss of all water content. Even DRY greenware has miniscule droplets of water within the clay platelets. That is why you need to vent the kiln during greenware firing – so that the moisture leaves the kiln as it evaporates.
In addition to the possible warping and cracking during firing, there is a strong chance that your resulting bisque will repel glazes and even some acrylic stains. That is because the entire piece has developed one big hardspot (the shell/crust). On smooth surfaced pieces, this can be avoided by removing the entire shell with a fine grit sanding cloth and then wiping it down with a damp (NOT WET) sponge to smooth out the traces of sanding marks. When you have a lot of details, it is not easy to get into the grooves and crevices, so you would have to use various cleaning tools which often results in loss of detailing.
When you do open the shell by removing the seam line, the under part is somewhat softer and if you apply water it will wash away the exposed area, but not the shell/skin, thereby leaving craters or grooves. If you are only striving to remove the seams, then DO NOT wipe the piece down with a damp sponge. I’m not saying you cannot clean old greenware, only saying that it is different and somewhat difficult. So much so, I tend to wonder if it is worth it.
Shop owners are encouraged to rotate their stock. If something begins to get old, clean the item and put it on a bisque shelf and double the price. Or, have a sale. Give larger discounts on the older items…get them out of your shop before they become so old as to be a problem.
How long does it take for greenware to get old? Well, that depends entirely upon your location. If your shop is not climate controlled, it will get old much faster than if it is in a heated/air conditioned environment. I recommend stock be rotated about every six months if not more often with sales, etc. If you have stock that is not moving for that long, it is time to change your selection anyway.
