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WSR - Wet Sieve Residue Test

A simple test of making a visual observation of how much residue, typically from a 50 or 100 gram powder sample, remains on a testing sieve after washing through a slurry of the material. This is almost always done as a quick way to assess material quality in comparison with past lots or shipments (e.g. of feldspars, kaolins, ball clays and silica), that is why a washing test is far more suitable (results are reproducable and it would be impossible to conduct a dry test at the fine sieve sizes needed). Since this test is normally done on many samples (e.g. from each pallet of a shipment), the technician simply makes a judgement call by comparing the amounts left on the wet sieve after washing, with the historically normal amounts.

Oversize Particles Simple Test

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This is simple test can be done to determine if oversize particles are present in a raw material to be used for clay body manufacture. While materials are sold as minus 200 mesh, as you can see here, they don't even pass at 150 mesh. In each case, we have attempted to wash through 50 grams of the powder (using the technique of our WSR test).

All ceramic materials must be ground using particle size reduction equipment. This process enables removal of contaminants or reducing their size enough that they do not marr the fired surface of the body. This is a demanding task. Being able to measure it quickly enables spotting problems with a materials shipment (and therefore how well a supplier meets their quality obligations and the kind of product that can be made using it). Ball clays and kaolins are the most problematic, not just in particle size and contaminating particles but also fired color and plasticity.

Of course, a record of this needs to be kept. That is where your account at Insight-live.com comes in. Upload pictures like these or just make a note of the result.

20 Skids of Material Just arrived

Fearful Freddie doesn't know what to do!

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Fatigue Freddie is scared. His company doesn't take responsibility for product quality variations resulting from material variations. But when it happens he gets blamed anyway. Production wants to start using it tomorrow! He doesn't test all the product runs they make. He doesn't test incoming materials. He doesn’t know how he would handle the mountain of data that world produce, or how to learn from and act on it. Plus he's alone, there is no cooperation between production, sales, QC in feeding info into any kind of record-keeping system.

Minimal testing: Give the shipment a new code in the recipe area of Insight-live. Enter what is known. Upload a picture of any certificates provided with it. Are all the pallets lot numbered? Record that in the notes. Are they all the same lot? Record that. Are the pallets sequentially numbered? Test one from each lot for oversize particles (very important for clays). Make an SHAB test bar also, get it/them dry (in the dehydrator) and into the kiln overnight.

Oversize particles in a typical manufactured porcelain body

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Example of the oversize particles from a 100 gram wet sieve analysis test of a powdered sample of a porcelain body made from North American refined materials. Although these materials are sold as 200 mesh, that designation does not mean that there are no particles coarser than 200 mesh. Here, there are significant numbers of particles on the 100 and even 70 mesh screens. These contain some darker particles that could produce fired specks (if they are iron and not lignite); thank goodness in this case they do not. Oversize particlate is a fact of life in bodies made from refined materials and used by potters and hobbyists. Industrial manufacturers (e.g. tile, tableware, sanitaryware) commonly process the materials further, slurrying them and screening or ball milling; this is done to guarantee defect-free glazed surfaces.

Watch out for iron particles in ball clays

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These are the oversize particles (from the 70, 100, 140 and 200 mesh sieves) from 100 grams of a commercial ball clay. They have been fired to cone 10 reduction. As you can see, this material is a potential cause of specking, especially in porcelain bodies. It is not only wise to check for oversize particles in clays, but firing these particles will reveaal if they contain iron. A 200 mesh screen would be a good start for this test, it would catch all of these.

This is what labs use to measure particle size

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To measure particle size in a slurry or powder you need sieves. This is the most popular type used in labs. They are made from brass by a company named Tyler. The range of screen sizes for testing particle size is very wide (obvious here: the top screen has an opening of 56 mm, the bottom one 0.1 mm - the wires are almost too small to see). You can often buy these used on Ebay for a lot less than new ones, search for "tyler sieve". The finer sieves (especially 200) are fragile and more easily ripped. For potters it is good to have a 50, 100 and 150.

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