So What IS that Glaze??

I’ve had a lot of people contact me about the red glaze on the garlic pot in yesterday’s posting. This glaze is one of our class glazes developed by Bill van Gilder called ‘van Gilder Crocus Red.’ You can see it on his website along with a lot of his other cone 6 glazes.

I’ll also post the recipe below along with a photo of a little ewer done in the same glaze. The handle on the ewer and the top of the garlic jar are overdipped in clear which creates some really interesting movement and gold crystals if I’m lucky.

van Gilder’s Crocus Martis Red – cone 6

NC Soda Feldspar (I’ve used F-4 or Minspar)     46.7
Talc    16.9
Bone Ash    15.0
Silica    11.4
EPK    4.0
Lithium Carbonate    4.0
Bentonite    2.0

Total    100

Crocus Martis     8.5
Red Iron Oxide     3.0


Happy glazing!

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  1. Thanks for the recipe…I intend to try it.
    Should it be slow-cooled?

    • No – doesn’t matter. It’s not that temperamental. I do hold it at 1900 for 10-15 minutes on the cool down though. That seems to work better for me.

  2. It is beautiful. Just to confirm, this is an oxidation glaze? Also, what clay is it on? Thx, MJ

  3. I love this glaze. I wanted to mix a test batch but I could not find the oxide Crocus Martis. I ended up ordering a test batch from Now I want to mix a large batch for myself. I have 3 suppliers within 30 miles of where I live and none of them carry it. I couldn’t find it at US pigment either. Would you be so kind as to tell where I could find Crocus Martis.
    Thanks, Paula

    • I’m not sure it’s classified as an oxide, but my local supplier is Clayworks in Baltimore and that’s where I get it. If you don’t see it on their website, give them a call as they usually do carry it. Clayworks Supplies

      I believe that Bill is working with a major glaze manufacturer on coming out with his own glazes in powdered form, so once that happens, you should be able to purchase larger dry quantities to mix on your own if you wish.

    • American Pigments has both the red and the yellow forms of crocus martis

  4. Audrey Kaake

    Beautiful color Nancy!

  5. Brett

    I’ve tried the Crocus Martis Red glaze but find it’s coming out more brown than red.
    Any suggestions?

    • Mine was coming out a really unattractive brown in the beginning as well. When I mentioned it to my teacher, he immediately said it was too thin. I now mix it a bit heavier than my regular glazes – kind of like heavy cream. It doesn’t run unless put on very heavy right near the foot; at least in my experience. Also, fire to a hot cone 6 – tip of cone barely touching shelf. If fired cooler, it will go brown. I take my kiln up to 2185 and hold it for 15 minutes. If fired to 6 1/2 – 7, it maintains it’s integrity but changes to a red-orange hue. I prefer the deep cherry red and so stay at the hot 6. Also, if you’re running a computer controlled kiln, when cooling, try a hold of 15 minutes at 1900. It may be my imagination but I think this gives me a redder color. Let me know how it works out for you.

  6. Jim B

    Nancy G,

    Very interesting glaze information and the potential of a purple red is very desirable. Do you know if this is food safe?

    Also, I’m considering the Crocus Martis as an addition to my red earthenware terra sigillata.



    • Hi Jim – yes, it is absolutely food safe properly fired to cone 6. I’d be interested in hearing about your experiments with it in terrasig. It does seem a bit ‘gritty’ but is a marvelous color.

  7. Mike Anderson

    I’m a little confused by this recipe. At the bottom it seems to say to add 8.5% Crocus Martis 8.5 and 3.0 Red Iron Oxide, but the glaze is Crocus Martis??? I get the red iron at 3% but what does it mean to add the Crocus Martis?

    • Crocus martis is a glaze ingredient – I think it’s a synthetic form of iron oxide. It’s a purple-maroon color. You need to add 8.5%

  8. Pete Garmin

    Cool Glaze!

    Can Crocus Martis just be substituted for normal Red Iron Oxide? Wondering if it will improve consistency of normal iron red glazes?

    • Hi Pete – thanks for the response…that would be an interesting experiment. I’m pretty sure Crocus Martis is a synthetic, and you’d probably need more Crocus than RIO in a recipe, but that’s just a guess. Maybe I’ll try it as a sub in Randy’s Red (which always comes out brown for me no matter how thick and how slow cooled) and see what happens.

  9. Rod Harper

    Hard to get red from iron in oxidation. It appears that you with your Crocus Martis have had more success than I. I’m going to try your recipe!

    I experimented with Randy’s Red and like you I got mostly a dull ugly brown to start off. With further tests on High Water Red Rock clay I got bright redish orange iron rust color on the inside of the pots. Very nice! I reasoned that the inside surfaces were being sagered by the walls of the pot so I made a sager and fired a large pitcher in it. The results both inside and out were stunning. Of course it still isn’t fire engine red but I’m sure this is what Randy’s Red is supposed to look like. I wish I knew how to attach a photo.


  10. Connie sheets

    On the Van Gilder Crocus Martes recipe you
    Add both 8.5 if crocus martis and 3.10 of red iron oxide??

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