• Glazes

    Iron Saturate Glazes

    During the next few days I’ll be releasing a series showing how to create a glaze using Glazy and volumetric blending.

    The first step is familiarizing oneself with the glaze type. For this demonstration I’m interested in creating a Cone 10 Iron-Saturate Red microcrystalline glaze also known as “Kaki”, “Tomato Red”, and “Persimmon”. Some historically examples are Chinese Song Dynasty Ding Persimmon-glazed wares as well as many of Shoji Hamada’s works.

    For each search, Glazy shows Recipe Cards with photos as well as a Stull Chart. The Stull Chart has five major regions: Unfused, Matte, Semi-Matte, Bright/Gloss, and Under-fired. There is another area, Crazed, that overlaps the other regions. In the next step, I will create a Biaxial Test using the Stull chart as a guide.

    From the analyses of Iron-Saturate glazes in Glazy, it is not clear what the ideal amount of Silica and Alumina (and the Si:Al ratio) should be. So our first step will be to re-create the Si:Al Stull Chart with a prototype Iron-Saturate glaze. In an Si:Al grid we can only adjust the amounts of Silica and Alumina, so we must set in stone the other characteristics of the glaze. Looking at the analyses of recipes in Glazy, it is apparent that we will need a good deal of Iron as well as Phosphorus. For our fluxes, apparently some MgO is required. As an educated guess, or initial prototype Iron Saturate glaze will have variable Silica and Alumina, while the following are set for all glazes: KNaO 0.2, CaO 0.6, MgO 0.2, Fe2O3 0.22, P2O5 0.12.

    We will use volumetric blending to magically create 25 glaze tests from only 4 batches of glaze. The four corner glazes composed using the Glazy Recipe Calculator. The columns originate from the Origin so that each column represents a specific Si:Al ratio. It is decided to put the “Left” column in the Stull Matte Region, while the “Right” column is pushed close to the Under-Fired Region.

    Batches of 500 grams are created for each corner glaze, and the test glazes are mixed using volumetric blending with samples of 20mg. The tests are ready to be fired!

    Note: The “educated guess” for our initial prototype glaze is informed in large part by the amazing work of Carol Marians. Carol has posted 8 years of glaze research on her website at:

    I made a mistake on the Si:Al ratios for each biaxial column. The ratios should be approximately 4.3, 5.4, 7, 9.3, and 12.8

    Here are the results of the Iron-Saturate Biaxial. While the reduction firing with uncontrolled cooling results in brown, metallic surfaces, the oxidation firing with a controlled cool and hold at 1700°F (925°C) gives us more interesting results. The biaxial reveals that an Si:Al ratio of around 9-9.5 (the fourth column) promotes redder glazes. In particular, tile D4 (4th row, 4th column) seems promising.

    The oxidation firing schedule is adopted from Carol Marians, but simplified to:
    150°F/hr to 250°F (65°C/hr to 120°C)
    400°F/hr to 2050°F (200°C/hr to 1120°C)
    120°F/hr to 2250°F (50°C/hr to 1230°C)
    60°F/hr to 2290°F (16°C/hr to 1250°C)
    40°F/hr to 2310°F (4°C/hr to 1265°C)
    Hold of 10 minutes at 2310°F (1265°C)
    400°F to 1700°F (925°C) – Down-fire
    Hold 2 hours at 1700°F (925°C)

    See for many more examples of firing schedules for iron red glazes.

    From the Iron-Saturate Biaxial we choose tile D4 to work with.  We can now “zoom in” and refine the Si:Al ratio for this tile.  At Si:Al 8-8.5 the glaze seems more evenly covered in crystals.  As the Si:Al ratio is increased the coverage becomes more splotchy.

    It seems the Si:Al ratio for biaxial tile D4 was already pretty good.  Now we can move on to testing factors other than Si:Al in the prototype glaze.  In this test, we increase the level of R2O (KNaO, or K2O & Na2O) while decreasing the amount of Calcium.  I was surprised by the result for 0.3 KNaO, perhaps there would have been a better result if both Calcium and Magnesium were decreased?  Or decrease Si & Al? Anyway, based on this test I’ll just stay at R2O:RO 0.2:0.8

    Test of Iron-Saturate Biaxial tile D4 replacing Mahavir Potash Feldspar with Minspar 200 Soda Feldspar.  Not a 1-to-1 percentage replacement, but maintaining the same UMF (except K2O and Na2O).

    Now that we’ve established an R2O:RO ratio of 0.2 using Potash Feldspar, we can test the best proportion of Calcia to Magnesia.  With our R2O set at 0.2, 0.8 remains for the RO (including Calcia and Magnesia) portion of our UMF fluxes.  The educated guess of 0.6 CaO and 0.2 MgO in our original Iron Saturate biaxial turns out to be a good choice.  More than 0.2 MgO also gives some interesting glazes with a more metallic surface.

    Same UMF, different sources of Magnesia.

    Glazes are often split into two parts:  A base glaze and additives like colorants and opacifiers.  It’s like ordering a pizza (base) with toppings (additives). We’ve already tested many aspects of the Iron-Saturate base glaze including Silica:Alumina, R2O:RO, and Calcia:Magnesia.  Now we can move on to the additives: Iron and Bone Ash. (The decision between what is part of the base recipe vs. an additive is somewhat arbitrary.  Just as with a pizza that’s made it to your stomach, it all eventually ends up mixed together.) Additives are added in addition to the base glaze recipe.  So in this test, I did not alter the base glaze at all, the only difference is increasing Red Iron Oxide and Bone Ash. I was surprised to see that additional bone ash didn’t alter the glaze a lot more.

    A line blend of biaxial test D4 blended with the same recipe without Bone Ash (but maintaining the same fluxes to account for the missing CaO from the Bone Ash). Without P2O5, our glaze is a nice tenmoku.  At 0.03 P2O5 very faint traces of crystallization appear.  At 0.06 P2O5 crystallization is much more evident, and somewhere between 0.06 and 0.09 P2O5 there is a dramatic transformation.

    Testing different sources of iron using tile D4 from the Iron-Saturate Biaxial.  I’m not sure what’s going on with Yellow Iron Oxide.  It would be interesting to see other sources of iron, especially iron phosphate.

    Adding Titanium Dioxide in 1% increments to tile D4 from the Iron-Saturate Biaxial. Titanium Dioxide is often present in analyses of Song Dynasty Russet/Persimmon glazes as well as Japanese Kaki glazes, but usually in amounts of less than 1%.

  • Techniques

    Mixing plaster in a plastic bag

    I’m not a plaster master, so I don’t know if this is a good or even original idea.  By mixing plaster in a plastic bag, it seems easier to remove bubbles from the mixture, while pouring is much more controlled.  It’s the same idea as using a garden watering can for pouring glaze:  You pour from the bottom where pressure is highest and bubbles are fewest.

    Add measured amount of water, then plaster into plastic bag supported by bucket.

    Let sit for a minute or two, then stir for about 5 minutes, being careful not to entrail air into the mixture.

    Lift the bag out of the bucket, checking for leaks.

    Check for air bubbles in the mixture.

    Air bubbles trapped in the plaster mixture.

    Pat the plastic bag, vibrating the air bubbles to the top.

    Cut a small corner off the bag, and control release of plaster using fingers. Pour in a controlled fashion against a wall without splashing.

  • Glazes

    Cone 6 Oxidation Blue Triaxial Blend

    In Chinese Glazes, we learn from Nigel Woods that the cobalt used for underglaze blue & white underglazes and blue glazes came in a range of chemical compositions and grades of purity.  Thus, there are many shades of blue due to the quality of cobalt-containing stone as well the overlying glaze.

    In the same book, Nigel presents a lovely Chinese blue stoneware glaze which, in addition to cobalt, contains iron and manganese “impurities”.

    In fact I’m personally not fond at all of glazes and underglazes containing only cobalt as a coloring oxide.  Pure cobalt often comes out as a garishly blue color.  In the triaxial blend below, I take a nice clear glaze (Sue’s Clear) with added 1% Cobalt Carbonate.  Then I blend with 1.5% Red Iron Oxide (bottom left) and 1.5% Manganese Dioxide (bottom right).  The resulting colors on the bottom row are much more pleasing to my eye.

    The full image can be viewed here:

  • Glazes

    Orton Cone 6 Clear Glazes

    Having not fired cone 6 since college, I started by first testing a number of clear cone 6 glazes on

    I also studied up on cone 6 glaze chemistry via Matthew Katz​’s Advancing Glazes course and his papers: Boron in GlazesMid-Temperature Glaze ScienceGlaze Safety/Durable Glazes Presentation.

    Click here for full image of cone 6 clears.

    Out of these tests, there were two glazes that I preferred.  The first, Sue McLeod​’s Clear, is a soft clear with minimal clouding and has B2O3 at 0.18 which, according to Matt’s information, is ideal for cone 6 glazes.

    The second glaze is a shop glaze available at the Wellsville Creative Arts Center called WCAC Celadon Clear.  With B2O3 at 0.45, it is really high in boron and possibly less durable than the lower-boron clears I tested.  However, WCAC Celadon Clear is by far the clearest glaze I’ve tested, almost like a layer of pure glass or honey.  Even on dark stoneware it’s really clear with almost no clouding.


    Sue's Clear on cone 6 porcelain

    Sue's Clear on cone 6 Brooklyn Red

    WCAC Celadon Clear on cone 6 porcelain

    WCAC Celadon Clear on cone 6 Brooklyn Red

    Being new to cone 6, I was curious as to the effect of boron levels on clear glazes.  So, I created two biaxials, both with R2O fixed at 0.2.  In the first Sue’s Clear inspired biaxial, B2O3 is set at 0.18.  In the second biaxial inspired by Celadon Clear, B2O3 is doubled to 0.36.

    Each biaxial resulted in a nice clear, with the higher Boron clear being almost completely transparent and glossy, while the Boron 0.18 clear is translucent and soft.

    Standard Cone 6 Porcelain Body #551

    Link to full-size image here.

    Same chart but with words describing each test glaze:

    Best Clear at B2O3 0.18

    The best clear resulting from the B2O3 0.18 biaxial is here: C6 R2O 0.2 B2O3 0.18 Best Clear

    B2O3 0.36 Biaxial

    In order to test the effect of higher B2O3 levels, I doubled the amount of Boron in the initial biaxial from 0.18 to 0.36 while maintaining the same R2O:RO ratio.  I also made the boundaries of the tests a little higher (see map comparison).  I was surprised to see that the only clear glazes in the 0.36 Boron test appear much farther down (lower in Si & Al) in the chart.  But the “clear” region is still in the same Si:Al Stull region.

    Link to full size image here.

    Best Clear at B2O3 0.36

    The best clear resulting from the B2O3 0.36 biaxial is here: C6 R2O 0.2 B2O3 0.36 Best Clear

    It is similar to WCAC Celadon Clear in it’s glossy, transparent quality.

    High-Boron Clears

    After testing WCAC Celadon Clear and seeing the results of my B2O3 0.36 biaxial, it seems there is definitely a region of very glossy, very clear glazes at higher boron levels.

    Coincidentally, I tested an old glaze recipe posted to the Clayart mailing list by Laura Speirs in 1996:  As with the WCAC Celadon Clear, the Speirs recipe is also very high in Boron (0.51), and it also fires very clear and glossy:


    VC Easy Glossy

    One afternoon I began discussing the WCAC Celadon Clear with a WCAC member, Nancy Alt.  I was very surprised to discover the interesting history of this glaze.

    In 2009 Nancy Alt had visited Val Cushing’s home and purchased a vase with a lovely blue-green celadon glaze. Nancy asked Val if he could share the glaze recipe, and he not only shared it but converted it from cone 9 to cone 6 (the temperature Nancy was firing). Val’s email is copied below. It shows the extremely generous nature of this amazing potter and teacher:

    From: Val Cushing

    Subject: Re: celedon glaze

    Date: May 12, 2009 at 12:46:57 PM EDT

    To: Nancy Alt

    Dear Nancy,

    This glaze is one I made for C/9 oxidation electric firing, so that it would appear to be a blue green celadon. I have revised it for you to be the same color and texture only for C/6 ox. electric . I will give you two to try , first VC Pale Emerald, C/6 , glossy , blue/green , celadon looking. as follows………. Kona F/4 feldspar 24, Ferro Frit 3134 24, Dolomite 4, whiting 14, barium carbonate 2, zinc oxide 2, flint 24, and EPK 6. ADD TO THAT , 1/2 % COPPER CARBONATE for blue green. VC/easy glossy, C/6 ox. , electric , celadon looking , green. Cornwall Stone 46, Gerstley Borate 20, Ferro Frit 3124 26, Ball Clay 8. — add 2% copper carb. and 1/2 % red iron oxide for celadon looking green color. Test these two Nancy and if the color is not exactly what you expected let me know and we can make a revision. We may have different “tastes” about color , but we can get what you want…My pale emerald should be quite a bit like the glaze on the jar of mine you now have. and THANK YOU . Val

    So it turns out that the glaze I liked so much, WCAC Celadon Clear, was actually a Val Cushing recipe called “Easy Glossy”.  I checked Cushing’s Handbook for the recipe and didn’t find it.  Nor could I find similar recipes in the Glazy database.  So it’s quite possible this is a newly discovered Val Cushing glaze recipe.

    However, the WCAC Celadon Clear had been modified from the original “Easy Glossy”, most notably subbing Gerstley Borate for Gillespie Borate.  I wanted to see not only the original recipe but also the color variations that Cushing was working with.  So I created a triaxial blend.

    Below is the triaxial blend using Copper Carbonate and Red Iron Oxide.

    Click here for Val Cushing’s “Easy Glossy” on

    Click here to download full size image.

    From Safety & Durable Glazes Presentation

    From Boron in Glazes

  • Tests

    Tichane’s Tests

    Some of Robert Tichane’s glaze tests and reproductions of Chinese Glazes donated to the Freer and Sackler Galleries:

    Glaze sample: Jun with copper red; Small bowl with two copper-red spots on outside, two on inside

    Modern reproduction of Yaozhou ware bowl from original mould in Metropolitan Museum of Art

  • Craft

    72 Hands

    From the Tiangong Kaiwu (天工開物) encyclopedia compiled by Song Yingxing (宋应星) at the end of the Ming Dynasty comes the oft-cited quote:


    For the total work required to make a single cup, it must pass through 72 hands, and only then can it become a vessel.

    72 Hands is an effort to document all types of ceramics techniques.  The video style is very simple- a single take of each technique focusing on the artisan’s hands.  Each video is accompanied by an article with a description of the technique and photos.  Videos are shot in high-resolution 4K Ultra-HD resolution which gives a clear view of the technique.

    Support 72 Hands

    To support the continuation of this documentary series, please consider becoming a patron.

  • Techniques

    Plaster Bats for throwing

    To be updated.

    Throwing large pieces on plaster bats reduces cracking issues.


    Using chamois leather to attach a plaster bat to the wheel

    Large sheets of chamois leather for drying cars can be purchased online very cheaply.  Synthetic versions that I have tried do not work.


    Cut a piece of chamois leather slightly larger than the wheelhead.

    Soak leather in water and position on the wheel head.

    Using a rib, scrape out water while the wheel slowly rotates.

    The leather is now completely attached.

    Pour a pool of water or thin slip on the leather

    Dip the plaster bat in water for a few seconds.

    Firmly place bat in the center of the wheel, wiggle until secure.

    When finished throwing, pry off the bat using a flat tool.

  • Techniques

    Working with a mirror

    A potter friend once made fun of me for using a mirror. But no matter how much I improve, I don't think I'll ever stop using a mirror when I throw and trim.

  • Techniques


  • Antiques

    Nothing new under the sun..

    With 10,000 years of history, there’s really never anything new in ceramics, just reinterpretations of the past.  Bowl base fragmentEdo period, Takeo Karatsu type.  Freer & Sackler Galleries.

  • Traditional

    Traditional celadon

    Recent firing with traditional porcelain stone glaze.  In the past I’ve tried but failed to use modern materials like feldspar and kaolin to capture the beautiful, unctuous surface and depth of porcelain stone celadons.  In this glaze the coloration is completely due to iron occurring naturally in the material.

  • Techniques


    I use X-acto blades all the time, some modified for specific tasks like carving porcelain or scraping glaze off of feet.

    I’m not sure if it’s all part of a vast X-acto conspiracy, but it seems that a lot of people don’t know that these blades can be easily & quickly sharpened?  While there are a number of sharpening methods (even just using bare fired porcelain) that will work, it can be tedious to get the sharpening angle right.  The most convenient method I have found is an angled sharpener (pictured).  Just a few quick passes through the ceramic sharpener gets the blades useable again.  It’s faster for me to sharpen the blade than switch out a dull blade for a new one.  (Unfortunately my sharpener is approximately 45% degree sharpening angle (> 20 degrees per side), it might be better to have a narrower-angled sharpener.)

    Also note that not all X-acto blades are stainless steel.  You don’t want rusty blades all over your studio or in your reclaim.  A 10 or 100-pack of stainless steel #11 blades might last you a lifetime.


    A step up from the X-acto blades are stainless steel surgical blades.  They come in a wide variety of shapes and sixes perfect for a number of jobs.  I usually use the blades without a handle.  They come in ten-packs and last a really long time if you sharpen them.

  • Techniques

    Pouring Glaze with a Watering Can

    I’m sure that using a garden watering can for pouring glazes is a common technique, but when I came up with the idea I thought I was a genius 🙂  The design of a watering can ensures a constant, strong stream of liquid during pouring that is perfect for glazing.  Bubbles are reduced since the watering can pours liquid from the bottom of the can.

    Adjust the specific gravity of the glaze. Here, a 250ml beaker is zeroed-out.

    The weight of 250ml glaze is 386.7. Dividing by the weight of water, 386.7/250 = 1.55. For this glaze, 1.5-1.6 is a good pouring thickness.

    Filling a watering can with glaze.

    Rotating the piece with your hand, maintain a continuous pour of glaze.

    You might need to rotate the piece backwards and forwards two or three times.

    Using a brush with watered-down glaze, fill in any holes.

    Glaze must be sufficiently watery in order to be absorbed into the hole.

    Glaze will inevitably end up on the outside of the piece. First scrape with a blade or metal rib.

    Finally, sponge off any glaze that remains on the outside.

    Pouring the Outside

    Once the inside is glazed, I will wait until the next day to glaze the outsides.  It’s important not to overload the bisque ware with water.

    I use an old electric wheel for pouring the outsides.  It’s important to rotate the wheel at sufficient speed so that glaze does not gather on the inside rim of the pot.

    Here’s a good video by John Britt about pouring the outsides on a turntable.

    Plastic strips are inserted into the splash pan to prevent glaze from spraying outwards. A heavy plaster model is tap-centered on the wheel.

    A soft piece of sponge is placed on top of the plaster to protect the inner glaze surface.

    A bowl is placed on top of the plaster model and tap-centered.

    The watering can is used to pour glaze starting from the foot. My finger stabilizes and prevents glaze from running into the foot.

    The application properties of your glaze will determine the amount of time the glaze should be poured. For this celadon glaze with an SG of 1.48 I pour from 4-5 seconds. Keep the wheel turning after glazing to ensure excess glaze is forced from the rim.

    Once the glaze has lost its glossy sheen, scrape off glaze from the bottom of the foot with a rib.

    Using a wet, clean sponge, clean off remaining glaze from foot.

    With sufficient wheel speed, the glaze should not gather too much on the inside of the pot. Once dry, excess rim glaze can be scraped off.

  • Craft

    Orton vs. Chinese Cones

    Well, that didn’t work out.  The kiln master ended up over-firing, past Chinese cone 10.  Orton cone 12 probably dropped around Chinese cone 8/9.  Looking forward to doing a better test in my own kiln.

  • Techniques

    Low-fire Electric Kiln

    I’ve finally gotten a new low-fire electric kiln.  This kiln is designed to fire up to 1000°C, so it’s useful only for on-glaze enamels and bisque.  Total cost was 2900RMB, which is about $420USD.

    The kiln uses 45cm X 50cm shelves, a common size here.

    Elements are also snaked through the bottom of the kiln, on top of which are placed bricks.

    Single K-type thermocouple placed in the middle of the kiln.

    Locking wheels, really handy.

    Control box.

    Element connectors

    Spring door.

  • Techniques

    Slow drying

    I have a couple “wet boxes”.  These are plastic bins with lids into which a layer of plaster has been poured.  The plaster is kept wet in order to maintain humidty, slowing (if not stopping) the drying process.

    However, I haven’t used the wet boxes in a long time.  I’ve found it much easier and more convenient to simply wrap each piece in it’s own plastic trash bag.  Pieces stored in this manner can be trimmed weeks or even months later.

    Ware placed on MDF bats and wrapped in plastic trash bags.

    Ware is placed mouth-down on an MDF board to prevent warping. The boards mold easily, alternatively only wrap the ware.

    After two months the ware is still wet, although the moisture is now distributed more uniformly.

    Bags of clay are double-bagged in large heavy-duty plastic bags. A piece of soaked plaster is placed in the bottom of the bag.

  • Techniques

    Kiln & Firing

    This page is in progress and will cover my kiln and firing.  For now it is just a place to store my notes.

    A typical 47kg/100lbs LPG propane tank used for firing gas kilns. Depending upon firing style, a small kiln requires 1 to 1 1/2 tanks per firing.

    The older bottles can be very dangerous. Sometimes the top pressure-release valves leak, even after closing.

    Hydraulic hoses connect the tanks to the gas line.

    In my experience, the hose connector is the most likely point of failure. Earlier models of hoses were just rubber and would start leaking at the connector after about 2 years of use. The rubber cap ring must also be regularly replaced.

    The first gauge measuring pressure directly from the tanks. Newly-filled tank pressure usually varies from anywhere between 0.2-0.6 MPa.

    Electric water heater and gas filter.

    Typical gas line connector. Inside each end is a rubber collar and plate that under pressure should eliminate leaks.

    The pressure regulator reduces the gas pressure to a level we can use in the kiln burners. I have mine set at 0.05 MPa.

    Gauge measuring outgoing pressure from regulator.

    Kiln room valves. The bottom lever valve can be used for coarse adjustment, while the top (needle?) valve is good for fine-tuning.

    The final gauge measuring pressure at the kiln. A typical firing rarely goes above 0.02MPa.

  • Glazes

    Colors of Celadon: Iron and Titania

    Following images from Bonham’s 2014 auction, The Feng Wen Tang Collection of Early Chinese Ceramics

    A Qingbai incised conical bowl

    A Fine Yaozhou Celadon 'Peony' Carved Bowl

    The best resource I’ve found about color in Chinese glazes is Nigel Wood’s Chinese Glazes.  Chapter 8, Iron in Chinese Glazes, covers iron in detail, while celadons are covered throughout the book.

    There’s a great range of colour in Chinese celadons.  In traditional celadons, color is mostly the result of materials containing naturally-occurring iron being fired in a reduction atmosphere, with the color modified by the balance of other oxides in the glaze as well as the underlying clay body.  Relatively small amounts of titania, manganese, copper and even cobalt can affect the color in significant ways.  Ancient kilns like Yue, Hutian, Longquan, and Yaozhou became associated with certain colors and qualities of celadon, as the materials used at those kiln sites naturally contained particular blends of oxides.  In Jingdezhen, celadon glazes seem to have evolved from fairly simple geographically specific material-based recipes (e.g. 10 parts glaze stone from Yaoli, 1 part glaze ash from Leping) to extremely refined and intentional recipes with similar base glazes that incorporate additional materials for their specific ability to modify color.  This lead to glazes named not just for kiln sites but also specific colors and qualities:   天青 (sky blue with a small < .2% addition of cobalt),豆青(”bean” celadon pure green iron celadon),影青(”shadow” lake-green),粉青,玉青 (jade celadon),冬青 (winter green),鸭蛋青 (bright duck-egg green), just to name a few.

    But celadons in the Song dynasty were mostly restricted to local materials.  Thus if your local clay and glaze stone contained only trace amounts of titania and low amounts of iron (such as in towns near Jingdezhen), then you could produce the famously pure blueish-green qingbai glazes.  While if you were in the Northern Yaozhou kilns where materials naturally contained more titania, your celadons would tend towards olive-green.  (These are greatly over-simplified and generalized statements.  Regarding Yaozhou celadons, in Chinese Glazes, Chapter 6, The Stonewares of North China, Woods also mentions the blueish-grey glazes of Yaozhou, as well as the possible influence of coal firing on the color of Yaozhou celadons.)

    For me, part of the beauty of Chinese ceramics is the ability of those ancient potters to reveal the beauty of their local materials, and how the resulting aesthetic of each kiln’s wares was in large part driven by the nature of those materials.

    Of course, these days most of us make glazes by blending various “standardized” materials, with color variations resulting from additional coloring oxides.

    The following test is a simple biaxial blend showing the influence of iron and titania on the color of a base glaze.  I’m now using Pinnell Clear for all of my additive tests as I find it a much better glaze than the traditional Leach 4321.  Further tests could be done using small amounts of manganese, copper and cobalt, as well as varying the fluxes and silica:alumina ratio.  For this test I substituted Grolleg for New Zealand Halloysite, but I did not adjust the recipe to account for the slightly different chemistry.  For this test it is important that the base glaze has as little titania as possible, so it’s best not to use “dirtier” clays.  The test tiles are made from Jingdezhen “super-white” porcelain, which serves as a good blank canvas for the glaze colors.  These glazes look quite different on dirtier porcelains and stoneware.

  • Glazes

    Glazy: One Year Old

    One year old!

    Exactly one year ago, Glazy registration was opened to the public. Since then, we’ve made a ton of improvements and added many more recipes.

    Thank you!

    94% of website server fees have been paid with your generous donations. Thanks to all of you who have added recipes, photos, and contributed valuable ideas to Glazy. Special thanks to Pieter Mostert and Matt Katz for all their help.

    Notable new additions to Glazy:


    Stull SiO2:Al2O3 Charts

    Si:Al Charts now include a Stull overlay as well as color-coded R2O:RO Ratios. To learn more about Stull, R2O:RO ratios, and other illuminating aspects of glazes, see Matt Katz’s Introduction to Glazes Online.


    Extended Search

    Simply click the eyedropper icon or one of the photo swatches to search by color. Keyword search is now greatly improved with natural language text search and the ability to search for numbers.


    Material Safety Information

    Newly added this month are hazard warnings for each material in the recipe. There is still a lot of work to be done in Glazy to provide accurate, easily understandable safety information for potters.



    There are more improvements planned. The most important change in the next few months will be the addition of material lists, including regional and supplier lists. Material lists can be shared between users and rated.



    Ceramics recipes “do not travel well” and are very sensitive to differences in materials, preparation, application, firing, and cooling. The best way to compare, critique, and refine our recipes is to share photos of our results.

    If you have photos you would like to share but find the Glazy interface too complicated, contact us and we will help. If you represent a school or studio with a lot of tests, we can help add the photos and recipes for you.