I have heard it said that the decline and fall of the Roman Empire was caused by toxic lead glazes poisoning them all. Sounds like a good reason to keep things healthy.

I don’t like the idea of working with super-toxic materials, and I dont much like the idea of sellnig work that has toxic glazes. When I was testing glazes to use, toxicity was one of the things I struggled with, but I thought I had got it covered. And then yesterday, as I was mixing a new batch of my green glaze a studio-mate asked what was in it so I reeled off the list from nepheline syenite on down. Imagine my horror when she said

“Nepheline syenite is one of the worst! I used to use it but then someone at college told me that it was really toxic”

Cue discussion of what is toxic when, potters dying of/with manganese poisoning, having to reclaim lead-glazed work, connections between nepheline syenite and cyanide etc etc.

Much anxiety then ensued. Particularly as I had done my homework as best I could at the start and thought the recipes I was using were kosher. But. The recipe is based on an Emmanuel Cooper one, and he didn’t seem to be at all concerned about health and safety so I was easily persuaded that there might be  a problem in the house.

Luckily I had Linda Bloomfield’s book to hand. At the back she has a handy list of ‘toxic’ and ‘very toxic’ materials that I could re-check. Phew. Nepheline Syenite is not on the list. (She also helpfully comments that whilst many of the oxides used in small amounts to colour glazes are toxic, that once fired they are held within the glass body of the glaze – much as nuclear waste is stored(!). She doesn’t say how much oxide is too much, but that is another line of enquiry…)


Just to be certain I also checked it in another very useful book, the potter’s dictionary. This told me that Nepheline is a type of feldspar and did not say anything at all about toxicity. It looked as if I might be in the clear, but just to make sure I also cross-checked one of the materials from Linda’s toxic list. The relevant entry in the dictionary stated clearly that it was highly toxic. At this I breathed a sigh of relief and got on with mixing my glaze.

After a testing moment my efforts to ensure that all of my glazes were non-toxic – both for myself working with the raw ingredients and also for anyone using them – seems to have paid off.


Featured image of natural nepheline syenite from here


2 thoughts on “Eek, one of my glaze ingredients is toxic!

  1. Your last paragraph states that Linda Bloomfield’s book lists nepheline syenite as “highly toxic” and goes on to say you breathed a sigh of relief. Did you mean to say the book lists it as non-toxic. I am confused.

    • Hi Lorrin,

      To clarify, nepheline syenite is not toxic. Another material I was cross checking for comparison is the one that is listed by both Linda Bloomfield and the Potter’s dictionary as toxic.

      Best wishes

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