If you want to go broke as a potter, try to get a red glaze.

February 13, 2024 9:12 AM

The Elusive Red Pottery Glaze Many types of asian pottery including the beautiful chinese red glazes of the Sung Dynasty and the exquisite Japanese Imari porcelain feature red as the main colour. The early Ming red is called “Sacrificial Red” because the Ming emperor kept the red-glazed vessels for animal sacrifices in sun worship. The Chinese associate red with the Sun. The secret for this sacrificial red was lost until modern science could decode found sherds via spectrometry. In the 1970s ceramic engineers in Europe developed a new generation of non-radioactive red colours and glazes based on a zircon encapsulated cadmium pigment.
posted by Lanark (21 comments total)

Interesting - yesterday was the impossible blue LED, today elusive red glaze...I wonder what tomorrow's difficult color will be!

(Both posts have been very interesting)
posted by Greg_Ace at 9:50 AM on February 13 [3 favorites]

Why did they not tell us students in 1970, Kent State metal arts and jewelry major, that cadmium was dangerous? We also all smoked like crazy in class and rested our cigarette buts on the solid asbestos work tabletop, asbestos being flame resistant when we were using a soldering torch...
posted by Czjewel at 9:52 AM on February 13 [3 favorites]

In high fire reduction environment kilns, one of the great crapshoot joys is the weird relationship between green and red. Not sure what explains it, maybe copper-based glazes? Have never been a person to look much into glaze formulation but that magic zone where a glaze might be clear or green or red is a blast! (If you don't value consistency.)
posted by kensington314 at 9:56 AM on February 13 [2 favorites]

"solid asbestos" is not dangerous, Czjewel its only when it's particulates get into the air and into your lungs that it will harm you. so hopefully that was never the case! cannot comment on the cadmium though...
posted by supermedusa at 10:23 AM on February 13 [2 favorites]

supermedusa, well that's a bit of relief!...
posted by Czjewel at 10:31 AM on February 13 [1 favorite]

I recently read a romance novel in which the FMC had developed a revolutionary red glaze for her family's pottery works and the successful marketing of pottery with that red glaze was a key aspect of the plot. This makes for some fascinating additional context on why red in particular.
posted by jacquilynne at 10:36 AM on February 13 [2 favorites]

When we lived in Massachusetts in the early 80s we did yard-sales on the weekend. I bought a lot of "diner china" (Buffalo mainly); my SO, with more refined taste, acquired loadsa Fiestaware. It wasn't until we returned to Europe that we were informed that Fiesta (esp. the reds) was radioactive. It's the uranium(IV) oxide UO₂. Still eating off it, although we only use the red plate for feast-days.
posted by BobTheScientist at 11:15 AM on February 13 [1 favorite]

I did pottery (ottery pottery) in high school and there was a mysterious bucket of glaze from generations ago called "Maybe Red" most of the time it fired to a dull greyish color but once in a while, perhaps on only part of a piece where the heat must have been *just right*, you'd get a surprising blush of real red. The nascent Discordian in me adored this celebration of the crapshoot that beginners ceramics always is, and I still have a piece with some of those splashes on it
posted by The otter lady at 11:25 AM on February 13 [26 favorites]

The otter lady flagged as fantastic
posted by kensington314 at 11:28 AM on February 13

There are glass colours that work like that, too, including a lot of reds -- I don't know what it is about the chemistry of red!

'Striking colours' they are called in lampwork. Sometime you have to work them at a specific temperature in the flame, sometimes you have to run them through different cycles in the kiln. I have a few rods of two different striking reds (as well as some striking oranges and some yellows that might be striking? I'm not sure.), but I don't actually know how to strike the colours and I don't have control of my own kiln, so I haven't tried to use them yet.

There are apparently two different mechanisms at work in striking colours -- some are different chemical structures that form when the glass is at a certain temperature and can be locked in if you cool it fast enough but if you cool it slowly it goes back to the original colour. Others have to do with the crystal size that forms when you heat and recool and the different colours that are reflected by different sizes of crystals and getting them to strike seems a bit like tempering chocolate.
posted by jacquilynne at 11:52 AM on February 13 [6 favorites]

Ah, TIL: striking

And here's a post about experiences striking: copper reds and strike firing
posted by Insert Clever Name Here at 12:07 PM on February 13 [1 favorite]

@the otter lady: seemingly, it's not the temp but the amount of available oxygen "Urania-based ceramic glazes are dark green or black when fired in a reduction or when UO2 is used; more commonly it is used in oxidation to produce bright yellow, orange and red glazes"
posted by BobTheScientist at 12:37 PM on February 13

It does occur to me that only in recent decades have I seen English style teapots glazed in bright saturated red. Greens and blues and browns are traditional.
posted by Aardvark Cheeselog at 3:07 PM on February 13

I pressure canned some beats from my garden and they turned white, and the liquid was clear. The heat must have altered whatever molecules that made the beats a deep red into something colorless. Cool! I wonder if they’re as nutritious.
posted by waving at 5:46 PM on February 13 [1 favorite]

The red pigments in beets (betalaines) are sensitive to high temperatures and can transform into a colorless compound during canning. Some varieties are more sensitive than others. The reaction is reversible and often the color of the canned product will return to a darker red after a few days of storage at room temperature.

Cool! #TIL...
posted by Greg_Ace at 6:33 PM on February 13 [4 favorites]

Shoot, I almost forgot to use my favorite SCIENCE! gif.
posted by Greg_Ace at 8:07 PM on February 13 [1 favorite]

From the "encapsulated" link: uh.

The stain is further rendered safer-to-use by washing with water or weak acid to remove any soluble uncombined compounds (e.g. cadmium or soluble impurities). This washing process does produce toxic byproducts that can only be tolerated in certain countries (e.g. India, China).

posted by away for regrooving at 10:38 PM on February 13

This washing process does produce toxic byproducts that can only be tolerated in certain countries (e.g. India, China).

That likely explains why the vast majority of red pottery is now produced in China. Though there is no reason why the stains couldn't be produced in China and then exported for use at potteries in other countries - leaving the pollution behind in Chinese rivers.
posted by Lanark at 1:47 AM on February 14

yesterday was the impossible blue LED, today elusive red glaze...I wonder what tomorrow's difficult color will be!

I collect Fiestaware and the most sought-after modern color is Lilac, because it was only produced for a very short time, allegedly because it was such a difficult glaze to produce consistently. They don't seem to have any problems with the reds though!
posted by biblioPHL at 8:17 AM on February 14

→ Shoot, I almost forgot to use my favorite SCIENCE! gif.

Magnus Pyke grew to loathe that experience, btw.
posted by scruss at 9:26 AM on February 14

So I've heard, but a great performance is still a great performance.
posted by Greg_Ace at 10:00 AM on February 14