Dichroic Glaze and Neodymium!

Dichroic Glaze and Neodymium!

Dichroic glazes change color under different types of light. This is a very unusual property which in ceramics comes usually with the use of a rare earth metal called Neodymium.

Neodymium gives a glaze a pale purple color in sunlight and most types of light, but sometimes it appears closer to white, and under florescent light it appears light blue!

It's a bit of a novelty, but also happens to be a very beautiful color, and it's translucency can't be achieved in ceramic glazes using other materials.

Speaking with a glass artist about this, he reccomended trying Holmium, another rare earth metal with dichroic properties. Holmium changes from pink to blue in different types of light. Unfortunately for ceramicists we need a lot of it, like up to 10% typically for rare earths to give pale to noticeable colors. Unlike our transition metal colorants, such as Iron Cobalt Copper etcetera, which can give strong colors with just a fraction of a percent. So at about a dollar per gram Holmium quickly gets pretty expensive to experiment with. Blown glass is typically much thicker than a ceramic glaze, so I attribute this to why they can use far less colorant and in the thicker layer their color still appears strong, but if we make viscous glazes that can be applied an eighth to a quarter inch thick without running off the pot maybe we can get away with smaller amounts of Holmium.

In terms of glaze chemistry, Neodymium is most likely acting as an alkaline earth in glazes, aka an "RO" aka a "secondary flux". This means that in the large percentages used to color a glaze it can significantly alter the texture and qualities of the glaze, in very large percentages (over 20%) it could be capable of crystallising if we're willing to do all the math to figure out the chemistry of getting roughly half the flux to be Neodymium and in a glaze suitable of crystallisation, ie relatively low silica and alumina with about .5 Nd. The thought of a Neodymium Silicate crystalline glaze sounds pretty incredible to me, trouble is this material is not currently accounted for in glaze calculation programs as an RO, so the math required to test a glaze like this is kinda a ton of work.

I think another good use of Neodymium would be in an extremely viscous glaze, applying it very thick would probably show the color better I'd assume. It also seems to go well with Titanium.

Using this oxide in a crystalline glaze has, in my experience, made it less "overtired" and less likely to crystallize, this is a simple fix of just bumping up the zinc level, in my case from going from .5 to .55 ZnO was a fine solution since i am not able to account for Neodymium more precisely, this worked to get a nice crystalline glaze with 10% Neodymium.

Another thought about the colors this produces, its color is incredibly similar to the rare (and extremely expensive) gemstone called Alexandrite. When i first heard of Alexandrite I assumed its color was due to Neodymium, but apparently not, it is a "Chrysoberyl" mineral BeAl2O4. I've never heard of anyone using Berylium in a glaze, because its so rare and expensive, and if we could it would pretty certainly act as an Alkaline Earth flux, being in the second row of the periodic table, producing a clear or white glass, most likely an opaque white glass, most similar to using Magnesium as a flux. Anyway, Alexandrite has this dichroic color shifting property, and like Neodymium it usually goes from purple to blue under different types of light, though it can also appear green pink and red apparently.

Funny story, one day I was reading in my hammock in the front yard, and a guy walking by commented on some pots we have on our porch looking like traditional Appalachian folk pottery. It turns out he's a ceramic engineer who spent most of his career making artificial gemstones, and apparently he made the worlds largest known piece of Alexandrite, which he used to carry around in the back of his car, until a random stranger at a bar randomly asked him if he was familiar with Alexandrite, and he gave that lucky stranger the worlds largest Alexandrite crystal. I don't know if this story was true, but I believe it, and trust I quizzed this guy as intensely as i could regarding pressurised kilns, carbon vapor deposition (making artificial diamonds), and gemstone chemistry, and he thoroughly knew about all these topics.

I use Neodymium frequently on jewelry in my "Lilac Color Shifting Glaze", I use about 10% of it yet the color is still very subtle, tho Ive seen people get much stronger color with less Neodymium. It really is a unique and beautiful color, and this has been my most popular jewelry glaze for the past few years, so I'm not the only one who likes this subtle and interesting material.

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