What to do with all the broken ware and trims from slip-casting? Simple,really. Reclaim it.
More Details:Clay is a natural element and it can always be reclaimed to a liquid state for casting molds. It is important however, that you pay attention to its proper balance for optimum use. Please refer to the article “Conditioning Slip for Optimum Use”
You do not need a fancy mixer to make reclaim. Most folks use 5 gallon buckets and a heavy duty drill with a paint mixer/paddle. If possible, rig up some kind of frame to hold the drill or it will bounce around and damage the bucket not to mention that it will wear out your arms. But, if you have a slip mixer, all the better. You really need to mix it for several hours over all before using it.
There are several methods to reclaim your trims. Some people collect and save all the dried bits and use them to create good sized batches of slip. Other folks will keep a bucket with lid handy and fill it with about 1/3 water and then drop their trims the bucket, keeping it covered until they want to reclaim it. If you let all the trims dry out, you will ultimately have to soak them in water for some time before reusing them or it will take forever to work out all the ‘lumps’ by mixing.
Most often folks will reclaim small batches (2-5 gallons) and mix it with ready-made slip (2 parts ready made to 1 part reclaim; or even half and half). They do this in hopes to keep the slip from becoming out-of-balance; however, it is encouraged to always test gravity and viscosity because it is so easy to throw your balance off.
If you use old slip trims that may be dirty, you will need to send the reclaimed slip through a fine mesh sieve to remove any debris as these particles may get embedded in your ware and when fired leave holes as they burn out. Pay particular attention to trims that may have bits of plaster from mold scraping as these will definitely leave holes. Bugs, hair, leaves, etc. are all items that can fall into the trim and create issues. when fired.
The process is simple, but it is work. Add enough water to the clay to make it fluid. Mix it and mix it until you can break down all the lumps and the slip is smooth. Mix it some more. If needed, send the slip through a sieve – besides breaking down lumps, this will also help remove debris. Let it sit several hours or overnight. Mix it again.
Check the gravity. If you are going to add it to some already made slip, you can do it as soon as you have the gravity correct. After mixing with other slip, check the gravity again. Make sure the gravity is balanced before proceeding. Remember, if it is too heavy, add more water, if it is too light add more clay. From here, you need to make sure it is fluid enough, so check the viscosity. If it is too thick you may need to add sodium silicate or Darvan 7 or some other defloculant. If the gravity is correct, DO NOT add more water to thin it.
Adding defloculant is the hardest part of making slip or reclaim. It takes so very little and it is so easy to add too much. If you are only reclaiming a few gallons, you will only need to add a few drops (mixed in with about a tablespoon of water). You can always add more if needed, but if you add too much it is not easy to bring it back in balance, so add a small amount at a time. Once you have some experience though, it does become easier. Keep a record book showing how much trim, how much water, how much deflocculant and you will soon see a pattern.
A gallon of good ceramic slip should weigh 14.5 pounds (plus a smidge). And it should have a gravity ratio of 1.75. A simple way to check your gravity is to take a container that will hold one or two cups of slip. Place the empty container on a scale and calibrate the scale to indicate zero. Then add one cup of slip and check the weight. A gallon of slip should weigh about 14.5 pounds (plus a smidge). Divide that by 16 cups and a cup should weigh about .91 pounds.
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