Bort Generation Knee Bandage

A sieve shaker. Being more independent is now cool again. Actually, it is being forced upon us by necessity: Supply chain issues and skyrocketing prices of convenience glazes, bodies, engobes, etc. Independence involves using sieves. True, it is no problem for a potter or lab tech to manually coax a glaze slurry through a small 80# sieve. But real independence is about sieving in volume - clay bodies and casting slips. About making your own porcelains and sieving out agglomerates. The ultimate in independence: Sieving particulates from your own native clay slurries. And doing it at 100, 140 and even 200 mesh. That requires a sieve shaker. This one cost us less than $100 to make. Of course, a Tyler sieve (or similar) is needed, these can be purchased on Ebay or Amazon. And a vibration motor, some metal and hardware and a friend with a machine shop.

This cost about $40 and arrived in about a week. It appears to be well made. The first major issue is going to be the diameter, 7.75 inches (this does not match Tyler, they measure 8 inches). Another issue is that it is not as tall, creating a greater chance of spillover. The bottom flange is not as wide, that could be a problem if the sieve needs to stay firmly locked in place in a shaker.

Some simple equipment is all you need. You can do practical tests to characterize a clay in your own studio or workshop (e.g. our SHAB test, DFAC test, SIEV test, LDW test). You need a gram scale (accurate to 0.01g) and a set of callipers (check Amazon.com). Some metal sieves (search "Tyler Sieves" on Ebay). A stamp to mark samples with code and specimen numbers. A plaster table or slab. A propeller mixer. And, of course, a test kiln. And you need a place to put all the measurement data collected (and learn from it). An account at insight-live.com is perfect.

The fired bars on the left are Plainsman L215 (with the material we are evaluating). These are a subset of the test bars, cone 4, 2, 02, 04, 06 (top to bottom), ~2150F down to ~1850F. The overlay graph shows pairs of firing shrinkage/porosity lines generated from the data we have been measuring, the descending ones plot increasing density with temperature and the ascending ones plot increasing shrinkage. The further the line-pair intersections push left the lower the temperature needed to mature the clay. But the steeper the lines, the more volatile the material. This data shows L4496 is much less mature till 2050F but suddenly vitrifies and then melts beyond that. The appearance of the bars verifies this. The orange lines would be even steeper were it not for the high sand content. The sand is certainly responsible for the unusually low fired shrinkage up to 2050F.

These are the recipes and calculated oxide chemistries of two pottery glazes (as shown in my account at insight-live.com): The original problem recipe and an adjustment to fix it. Recipe #1 sources boron from a soluble material and three plastic materials are combined to increase drying shrinkage enough to cause cracking when drying (and thus crawling). Recipe #2 solves these problems while producing the same chemistry. It sources boron from two frits (one having almost no Al2O3) whose ratio to each other can be altered to supply more or less Al2O3 to the melt. That enables removing two of the plastics: Ball clay and Gerstley Borate. The remaining 20% EPK is perfect to create a creamy slurry that suspends, applies and dries well.

Lithium carbonate is now ultra-expensive. Yet the glaze on the left needs it. Spodumene has a high enoughLi2O concentration to be a practical source here. It also has a complex chemistry, but the other oxides it contains are those common to glazes anyway. Using my account at insight-live.com, I did the calculations and got a pretty good match in the formulas (lower section in the green boxes). Then I made 10 gram balls and did a melt flow test at 2200F (notice the long crystals in the glass pools below the runways). Not surprisingly, this recipe is very runny, that's why the tiny yellow crystals grow during cooling, they produce the gold effect this recipe is known for. The spodumene version is very similar, perhaps better. The calculated cost shown is outdated, in 2022 for us it is $17.84 vs $10.40 per kg (based on purchasing 2.5kg amounts of the materials).

This was applied at 2.5'' ID 4'' OD Performance Sport Great Sound Straight Exhaust M stage on Plainsman M370, 1917 Singer Sewing Machine Red Eye Model 66 Hinges & Screws fired on, dipped in clear G2926B glaze, then fired at Pink Hydrangea Flowers Artificial Silk Flower Bouquet Faux Hydra. The transfer was purchasing online. Since the pigment contains cobalt it does feather somewhat at the edges, this would be less of an issue at low temperature.

This is an example of cutlery marking in a cone 10 silky matte glaze lacking Al2O3, SiO2 and having too much MgO. Al2O3-deficient glazes often have high melt fluidity and run during firing, this freezes to a glass that lacks durability and hardness. But sufficient MgO levels can stabilize the melt and produce a glaze that appears stable but is not. Glazes need sufficient Al2O3 (and SiO2) to develop hardness and durability. Only after viewing the chemistry of this glaze did the cause for the marking become evident. This is an excellent demonstration of how imbalance in chemistry has real consequences. It is certainly possible to make a dolomite matte high temperature glaze that will not do this (G2571A is an example, it has lower MgO and higher Al2O3 and produces the same pleasant matte surface).

Why? Glaze fit. These are available on Aliexpress (as Drip Pottery or Drippy Pottery) and they are made by a manufacturer that has close control of body maturity (and thus strength) and the capability to tune the thermal expansion fit of glaze-on-body. It has to fit better than normal because of the absence of an outside glaze. Too low an expansion and the compression (outward pressure) will fracture body (these are thin-walled pieces making them vulnerable). Too high and it will craze. And the glaze is thick, it will shiver or craze with far less forgiveness than a thin layer. And how did they get the glaze on this thick? They likely deflocculated it, up to 1.7 or more, glazed the inside, let it dry, then glazed the outside. These pieces are a visual and technical achievement. If you are a potter you had best think twice before attempting the same.

Potters are used to making dipping glazes that they weigh out and mix from recipes. Hobbyists commonly use bottled commercial brushing glazes. Did you know that a dipping glaze can be turned into a brushing glaze by the addition of Veegum (or Veegum CER) and water? Do you know what a base-coat dipping glaze is? Here is a quick overview: Dipping glazes need to go on to Satin Band Luxury Double Sided Old Pink Dark 3 M On 1,6 CM Super ware evenly, be thixotropic enough to hold on at thickness and drain and dry quickly. But they don't need to dry hard. Brushing glazes need a cohesive slurry that dries slowly and hardens well on drying. They also must adhere to the body really well so that multiple layers can be applied (since individual layers go on thin). Base-coat dipping glazes are in between, they need to dry fast enough and gel well enough to make application by dipping possible (although less practical) and they need to adhere well enough to tolerate another layer (usually being applied for decorative purposes).