A gunmetal glaze I have wanted for decades!After 40+ years of making pottery I finally have a perfect gunmetal black. It has an incredible silky surface. It does not cutlery mark. It does not craze on anything. It is easy to clean. This is G2934Y with 6% Mason 6600 black stain firing using the PLC6DS schedule. I had to tune it a bit, adding ... more After 40+ years of making pottery I finally have a perfect gunmetal black. It has an incredible silky surface. It does not cutlery mark. It does not craze on anything. It is easy to clean. This is G2934Y with 6% Mason 6600 black stain firing using the PLC6DS schedule. I had to tune it a bit, adding about 15% glossy G2926B, because it was a little too matte on initial firings. But now it is perfect. These are heavy mugs made using the M340 casting recipe (and the casting-jiggering process). The speckled mug was made by casting a thin layer of the speckled version of the slip first, then filling the mold with the regular slip. I used a 40-minute cast to get walls nice and thick! Context: Cooling rate drastically affects the appearance of this glaze, Gunmetal glaze Sunday 2nd February 2020 
Why do these cone 04 and 6 clear glazes have so similar a chemistry?The glaze on the left (as shown in my account at insight-live.com) is a crystal clear at cone 04. The high frit content minimizes micro-bubbles. The high B2O3 melts it very well (this has 0.66 B2O3, that is three times as high as a typical cone 6 glaze). The recipe on the right is the product of a ... more The glaze on the left (as shown in my account at insight-live.com) is a crystal clear at cone 04. The high frit content minimizes micro-bubbles. The high B2O3 melts it very well (this has 0.66 B2O3, that is three times as high as a typical cone 6 glaze). The recipe on the right is the product of a project to develop a low-thermal-expansion fluid-melt transparent for cone 6 (with added colorants fluid melts produce brilliant and even metallic results and they variegate well). While the balance of fluxes (the red numbers in the formula) is pretty different, look how similar the B2O3, Al2O3 and SiO2 levels are (yellow, red and blue backgrounded numbers in the formula), these mainly determine the melting range. That means that a fluid-melt cone 6 glaze is actually just a low temperature glaze being overfired to cone 6.
Context: G3879 - Cone 04 Transparent Low-Expansion Base Glaze, G3806C - Cone 6 Clear Fluid-Melt Clear Base Glaze, What Determines a Glaze's Firing Temperature?, Fluid Melt Glazes Saturday 1st February 2020 
Is that recipe you found online really what you think it is?It contains significant Frit P-25, I googled that to Digitalfire, it contains 1.8% fluorine! When that gases off during firing are you really equipped to deal with fluorine gas in your studio? One answer is to substitute my own frits (which of course do not contain fluorine). I did the calculations ... more It contains significant Frit P-25, I googled that to Digitalfire, it contains 1.8% fluorine! When that gases off during firing are you really equipped to deal with fluorine gas in your studio? One answer is to substitute my own frits (which of course do not contain fluorine). I did the calculations in my account at insight-live.com (see the recipes side-by-side). In the formula, I substituted the F (fluorine) for a mix of CaO/MgO. In the recipe, I substituted Ferro Frit 3110 (it is also a high-sodium frit) for the P-25, then I juggled the rest of the recipe to match up the oxides. More Gerstley Borate supplies the lost B2O3, more ball clay supplies the lost Al2O3 and less silica is needed (because the ball clay brought along more). I ended up with a recipe that is going to suspend much better (more clay) and was able to eliminate the whiting (because the rest of the new recipe is supplying more CaO). This recipe has a high thermal expansion, that means crazing. Would it not be easier to simply add a red stain to a clear glaze you already have that is working well on your clay bodies?
Context: F, Trafficking in Glaze Recipes Saturday 1st February 2020 
Red burning, customer-found terra cotta clays testedWe tested four different clays (brought in by customers). One is from BC and three from Alberta. These fired sample bars show rich color, low soluble salts and high density and strength at very low temperatures. L4233 (left): Cone 06 to 3 (bottom to top). Reaches stoneware-density at cone 02 (middle ... more We tested four different clays (brought in by customers). One is from BC and three from Alberta. These fired sample bars show rich color, low soluble salts and high density and strength at very low temperatures. L4233 (left): Cone 06 to 3 (bottom to top). Reaches stoneware-density at cone 02 (middle bar). Plasticity is very low (drying shrinkage is only 4.5%). But, it is stable even if over-fired. L4254 (center bottom): Cone 04,02,3,4 (bottom to top). Very fine particled but contains an organic that is gassing and bloating the middle two bars. L4243: Fires lighter and looks stable here (cone 02,01,1,2 shown) but melts suddenly less than a cone above the top bar (well before vitrification is reached). L4242 (right): Hyper-plastic (12% drying shrinkage!). Already melting by cone 02 (third from top). Achieves almost zero porosity (porcelain density) at cone 04 (#2 bar). Even when mixed with 20% kaolin and 20% silica it still hits zero porosity by cone 1. What next? I'll mix L4233 (left) and L4242 (right), that should produce stoneware density at cone 02 (about 1% porosity). Context: Terra cotta, Soluble Salts, Drying Shrinkage, Vitrification, Bloating Saturday 1st February 2020 
Frit Melt Fluidity Comparison - 1800FFired at 350F/hr to 1800F and held for 15 minutes (I already did firings from 1300F-1750F in 50 degree increments, all of them are visible in the parent project). Frit 3110, 3134, 3195, F75 have run all the way down. All of the frits have softened and melted slowly over a range of temperatures ... more Fired at 350F/hr to 1800F and held for 15 minutes (I already did firings from 1300F-1750F in 50 degree increments, all of them are visible in the parent project). Frit 3110, 3134, 3195, F75 have run all the way down. All of the frits have softened and melted slowly over a range of temperatures (hundreds of degrees). By contrast, Gerstley Borate, the only raw material here, suddenly melted and flowed right over the cliff (between 1600 and1650)! But not before Frit 3602 and FZ16 had done so earlier. Frit 3249 is just starting to soften but F69 (the Fusion Frits equivalent) is a little ahead of it. LA300 and Frit 3124 are starting also. F524, F38, F15 will all be over the end by the next firing. The melt surface tension is evident by the way in which the melts spread out or hold together. Context: Frit, Comparing the Melt Fluidity of 16 Frits Friday 31st January 2020 
Cutting out the background on a photoWhite backgrounds are used for presentation on ecommerce websites (contextual backgrounds when showing a product in use). Even if you can photograph to pure white at the edges of a photo, it will transition to grey around the object and pieces will almost always have some fuzzy edges. While there ... more White backgrounds are used for presentation on ecommerce websites (contextual backgrounds when showing a product in use). Even if you can photograph to pure white at the edges of a photo, it will transition to grey around the object and pieces will almost always have some fuzzy edges. While there are automated edge-detection tools in editors like Photoshop or GIMP, they do not give clean edges like this. So professionals do this job using a vector-editing tool. In the past this implied learning the path tool (e.g. inPhotoshop) but now inexpensive phone apps can do it well. On the lower left is the original image (already cropped). On the lower right I have it open in an iOS app named Exacto. The blue dots are stationary anchors and the black ones pull out curves between them (curves flow smoothly through the black ones). By zooming and add/moving dots I can produce these crisp edges (Exacto saves it to iOS Photos with a transparent background). Notice how clearly the clean edges enhance the throwing rings on the right. Context: Bit Image, Tenmoku Friday 31st January 2020 
Adding a frit of unknown chemistry in a glaze recipe?That is like adding a dog of unknown breed to this team. How predictable is that going to be? It is like that with ceramic glazes. They fire the way they do because of their chemistry. Not knowing the chemical makeup of a key ingredient robs you of the single biggest tool to explain characteristics or issues or propose adjustments, improvements or fixes. Context: Glaze Chemistry, Frit Monday 27th January 2020 
Sedimentary clays are a whos-who of the periodic tableThese are the results of a detailed elemental composition analysis of a sedimentary clay. The first column of numbers is ppm (parts per million), divide them by 10,000 to get percent. The Fe here, for example, is 50,868 or 5.1%. The second column is +/- error. Notice that this test does not detect ... more These are the results of a detailed elemental composition analysis of a sedimentary clay. The first column of numbers is ppm (parts per million), divide them by 10,000 to get percent. The Fe here, for example, is 50,868 or 5.1%. The second column is +/- error. Notice that this test does not detect boron or lithium, they require a different method. By contrast, the chemical analysis shown on the data sheet of a typical ceramic material shows only the principle ceramic oxides (less than a dozen), but all of these trace elements will still be present. Context: Clay, Analysis, Glaze Chemistry, Toxicity Friday 24th January 2020 
Things that are too big to 3D print can be done in two piecesThis jigger mold shell has a step that provides the ideal place to split it into two pieces for printing. It is not necessary to do it in your 3D design app, 3D slicer software has the ability to do just before printing. In Simplify3D you just push the object downward on the platform (anything below ... more This jigger mold shell has a step that provides the ideal place to split it into two pieces for printing. It is not necessary to do it in your 3D design app, 3D slicer software has the ability to do just before printing. In Simplify3D you just push the object downward on the platform (anything below does not print). Prusa Slicer (and Slic3r) offer a cutting plane to cut an object in two (after printing the first piece you just undo to restore the removed half and then delete the first section and print the second). Then, after printing, just glue the two pieces together. Context: 3D Printer Thursday 23rd January 2020 
Cuerda seca is a flexible technique at any temperatureThe mug is has an unglazed (bare porcelain) outside surface. The cuerda seca lines containing the glaze have a formulation to flux and melt more than what is typical in the classic technique on tiles. And this appears to be reduction-fired porcelain at high temperatures (because of the iron specks ... more The mug is has an unglazed (bare porcelain) outside surface. The cuerda seca lines containing the glaze have a formulation to flux and melt more than what is typical in the classic technique on tiles. And this appears to be reduction-fired porcelain at high temperatures (because of the iron specks and grey body color and the metallic appearance of the lines), in contrast to the normal low fire terra cotta temperatures of typical cuerda seca. The formulation for the lines is likely very high in iron oxide (with some kaolin added for suspension, dry hardness, adhesion and paintability). The fill glazes are a transparent with added stain. Context: Cuerda Seca Thursday 23rd January 2020 | Contact Us:
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