Drying seems so simple that most people just ignore it. Most folks have drying problems, but approach the problem as if it were a problem of the ware or the manufacturing method. 

Most of the time drying problems can be solved rather simply, but one must approach them as if they were drying problems not ware problems. It seems easier to change the clay than to provide for a proper drying method. Once you know the fundamentals of drying, you might find it easier to make a change in the drying method to solve the problem. 

First lets look at simple basics of drying. Remember that it is really a lot more complicated than this explanation, but if you follow these basics, it will nearly always get you out of trouble. There are several things to consider in drying; the speed that water leaves the surface of the piece, the way that water gets to the surface and the way water is held in clay. The most important thing to learn here is that clay holds onto water much differently than non-plastics (like sand). If you were drying sand it would be very simple since the water leaves the surface readily and does not allow the material to shrink. Clay, on the other hand, has a strong bond with the water. In most cases there is more water mixed with the clay than is tightly held to the clay crystals. 

As soon as water leaves the clay the ceramic part shrinks to fill the space occupied by that water. Eventually enough water leaves a particular area so that the part no longer shrinks (in that area). 

It is also important to know that the shrinkage mentioned above occurs only at the spot where the water is leaving. It is for this reason that parts will warp or crack. For example, if you have a newly made piece just sitting on the shelf. Let's say its a dry (low humidity) day. The exposed surface of the part, for example the side facing an aisle, will dry faster. It will start to shrink more than the other side. Pretty soon there will be a crack develop. 

Another example, suppose you make a tile and place it on a board. The part cannot dry the same on the board side. It may dry faster at first, or slower. In either case the part will either warp or crack because of the uneven drying. 

Once enough water has been removed, the part will cease to shrink. At that point it can be dried faster with safety. 

Ok, to review, clay parts shrink as water is removed, they shrink more where more water is removed. So, to stop cracks and warps, dry evenly. Now you cannot always dry as evenly as you would like. In other cases you will find that if you dry to fast the inside will not evenly feed water to the surface. In that case the part will crack due to stresses inside the piece. So, now you need to know how to dry more safely. This requires knowledge of how the water leaves the surface of the clay. 

You also need to know about how water moves inside the clay. First of all, since the water inside the piece cannot move as fast as the water can leave the surface, it is necessary to know how to slow down the movement of the water away from the surface. 

There are only three elements involved in the formula for water leaving the surface. These elements are: air velocity (and direction), air temperature and percent relative humidity of the air. Lower velocity air dries more slowly, cooler air dries more slowly, and higher relative humidity dries more slowly. 

Lets look at that ware on a shelf. If it is a dry day (low humidity air) the thing to do is to make the relative humidity higher and to make the air more still. The easiest way to do this is to cover the shelf with some plastic sheet. It keeps the wind out and allows the local humidity to build up as the water leaves the ceramic. If the air is too dry, put a pan of water on the floor under the shelf in order to make the humidity go up. 

Once the piece as stopped shrinking you can open the shelf and even turn on fans. Heated air is ok at this point since you can safely dry faster. Warm air and a fan will dry the part much faster. Warning, do not do this until all the shrinkage has stopped or you will still get cracks. Now, to be more sophisticated, you could dry on moveable racks and move the racks into different rooms, or enclosed places, in which you have gradually reducing humidity and raising temperatures and air speeds. That will let you dry more stuff faster. 

One of the really nasty parts of drying is that if you do not dry properly you can get stresses that do not show up until firing. So, remember, some firing cracks are really drying cracks that didn't show up until firing. If, at the beginning, you use higher humidity you can gradually raise the temperature. Raising the temperature makes the surface tension of the water drop. You want the lower surface tension so that the water can move more easily through the small spaces inside the ware. You want it to get to the surface as quickly as the water being dried can leave the surface. 

To conclude this short note, try to place you ware in such a way as to allow the air to evenly get to all sides. Place flat tiles on an open grill, for example. Place long cylinders with the least surface contact possible and air movement along the part from one end to the other, not across the piece. The try to avoid drying conditions having air that is too dry and too fast in the beginning. There is a lot more to it than this, but we hope that this short e-zine information will help you reduce your losses. 

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