Crocus Martis

[Kim Estares]

i have heard that glazes mixed with Crocus Martis as your colorant should be mixed in smaller batches that over time that colorant breaks down. Does anyone know about this?  Im looking at mixing "Orange Street"

Thanks 

Kim

[Norm Stuart]

Orange Street is one of my favorite glazes.  I use a nice synthetic red iron oxide and yellow iron oxide - a hydrated form of red iron oxide which curiously retains its yellow color after firing, as it does in Strontium Crystal Magic Warm underglaze. (I would have expected the yellow hydration to be calcined-off). 

Orange Street glaze with synthetic red iron oxide and yellow iron oxide is shelf stable for longer than we've ever had it around.

To the best of my knowledge Crocus Martis was a natural purple red iron oxide which has not existed for many years, perhaps not for decades, similar to the original Cornwall or Cornish Stone.  Some say it came from a mine in Africa, others claim it was sourced elsewhere.

This Purple Ochre is a augite-porphry mineral from Armenia which is ground into a purple paint pigment you can purchase.  This mineral is primarily red iron oxide, but the crystals look purple because they supposedly have a larger crystalline size which reflects the light purple rather than red.  This purple color property may or may not survive a firing to Cone 6.  I've not used it.

http://www.amazon.com/Agulis-Pigments-Mineral-Pigment-Porphyry/dp/B...

http://www.naturalpigments.com/art-supply-education/purple-ocher-pa...

What passes for Crocus Martis today?

http://digitalfire.com/4sight/material/crocus_martis_249.html

http://www.nmclay.com/ProductDesc.aspx?code=CROCUSMARTIS

Jeff Poulter and I have both found the Bayferrox-180, which New Mexico Clay sells in place of the long lost Crocus Martis, fires somewhat less red than other synthetics at Cone 6 due to its smaller particle size.  More of the red iron oxide survives degradation at cone 6 in larger particle size synthetics, such as the "High Purity" from China, sold by U.S. Pigments.

http://www.uspigment.com/chemicals.shtml

Prominfer's Spanish Red Iron Oxide  is an unprocessed iron ore, some say concentrated by rain runoff in an iron mine in Spain, which creates a variety of yellow through red colors.

http://digitalfire.com/4sight/material/spanish_red_iron_oxide_2244....

Spanish Iron Oxide used in Spanish Nutmeg

My version of the Orange Street recipe in the Insight-Live glaze database.

Orange Street  

with Yellow Iron Oxide and High Purity Red Iron Oxide from U.S. Pigment

What is high-purity or synthetic Red Iron Oxide?

An inexpensive way to purify something is to crystallize it, as many materials naturally exclude most foreign material during the crystallization process.  So they crystallize Iron Sulfate.  The very pure Iron Sulfate is then fired with oxygen in a tunnel kiln which burns off the sulfur and oxidizes the iron to 98% or greater purity.

Other red iron oxides are typically only 2/3 red iron oxide with the balance being black iron oxide or a combination of the two resulting in a brown color.  Some impure ceramic red iron oxides even include barium sulfate to prevent scumming from the other impurities.

[Kim Estares]

Thanks Norman
This information was really helpful. I had questions about Spanish RIO too, so that was great. The bag I got of Crocus Martis was really old from a now defonked ceramic supplier that had been around for decades, so who knows what I've really got here. But I like stability in my glazes so I'll be ordering the synthetic RIO,

THANKS
KIM

[Norm Stuart]

It would be very interesting to compare a small batch of Orange Street with the Synthetic Red Iron Oxide and Yellow Iron Oxide, with one made with the original Crocus Martis, if you ever had some extra time, because most of us have probably never seen it in a glaze.

Since you're one of the few people in the world is an actual bag of Crocus Martis.  Our studio has a very old bag of Albany Slip so we can still make actual Albany Slip recipes.  So far the real ^6 Albany Slip glazes I've made are not that interesting.

Or do a comparison with a synthetic red iron oxide and crocus martis in a glaze like this Red Orange which was intended to be colored exclusively with Crocus Martis.  George Lewter notes he used Bayferrox-180 in his test tiles pictured.

[Kim Estares]

Hi norm
I'm not sure if I have the real deal or not ...its finer than RIO and a little oranger, closer to Spanish RIO. I'll be doing some additional testing once the synthetic RIO gets here, no violet visible in the dry form. I'm a ways out from having a kiln load of pots and my test kiln is not programable. I'll post findings when I get them done.

Thanks
Kim