[Joanna_Yle]

Hi everyone,

I am not a chemist and only have a basic knowledge of chemistry.
I am actually a potter and I am starting to make my own glazes from ingredients "picked in the field".

Ashes have been traditionally used as ingredient in glazes. For example tree ashes or seaweed ashes. I have read that in general, ashes contains different ingredients like calcium phosphate, iodine, potassium carbonate...

What interests me are the oxides and carbonates because they are the only way to create color when firing at high temperature (up to 2336 F or 1280 Celsius). I fire in oxidation.

So my question is: what oxides or carbonate would ashes from hair contains?
The oxides and carbonate that we usually use in ceramic are cobalt, iron, chrome and copper.
I also wonder if there could be any health hazard while using ashes in glazes? Could the resulting glaze release toxic compounds after being fired and cooled down when used as dish for food or a cup (such as heavy metals?)
I know I can always turn to a lab to test the toxicity, but i would do that when my glaze is ready!

Human hair (as disgusting as it might seem) is a readily available material as waste at hairdressers saloon, it is easy to burn to ashes and to turn into a powder to be mixed in glazes.
I have seen a video of someone dropping horse hair on a burning hot pot (outside of the oven), it made black burnt patterns. That is why i got to think about ashes from hair.

If you have any suggestion of natural materials that could yield interesting ashes for ceramics, I am also interested to hear your advice!
Plant material is easier to process because I don not have any ballmill,  stone-hard deposits are not an option yet. It could be natural plants (I live in Scandinavia so you get an idea of the vegetation : pine, spruce, beech, blueberries, reeds..) or harvest crops waste (wheat, barley, peas...) ?

Thanks in advance!

[Borek]

Hair are not heavily mineralized, so the amount of ash will be quite low, and as far as I am aware rather typical for ashes of organic matter. I would expect mostly boring oxides and carbonates of Na/K/Ca/Mg, nothing fancy.

[Joanna_Yle]

Thank you Borek for your rapid answer!

In a book I found that potassium oxide, sodium oxide and calcium oxide are potent fluxes in glazes, so they basically lower the melting point of glass and makes the glaze runny. Too much fluxes and the glaze drips from the pot and its wasted (when cooling down it solidify with the kiln shelves and you must hammer it away).

Magnesium oxide, is a flux as well, and in large amount will make an opaque smooth surface. So lets hope there is enough magnesium oxide to get some effect

I also got to think : about about the hair dies people use : can they contain any oxides?

About the amount of ashes: to make a test batch I would need about 50 grams of refined ashes.

[AWK]

Total ash content of human hairs is below 1%. Main metals in ashes are Ca and Mg, much less Fe and Cu.

[Joanna_Yle]

Thanks AWK. Okay so I need to burn at least 5 kg of hair, for 50 grams of ashes, lots of work! Feasible for a test, but definitively not for producing glazes to put on pots!
That puts an end to the hair ash glaze... I might try just to see what it looks like.

Iron oxide yields a brown red, and copper oxide a nice green. The amount of oxide for the color to appear is 2 to 5 % of the dry weight. So it might still be too low concentration to show up as a color.

So, has anyone an idea of what natural material could contain enough oxides to make some color in glazes?
What about mushrooms? What would burnt mushrooms contains? (it is full season right now here!) I am really open to any idea of material to use!

[Borek]

I am afraid most natural material (and by that I mean organic material from plants or animals) will be quite similar. The only things with high mineralization are bones and teeth, but they too contain mostly the same boring set of metals. The only difference is that they are made not of carbonates, but of phosphates.

[Arkcon]

All living things contain some traces of minerals, but that's mostly just it...traces.  There are exceptions, but they're rare, and almost impossible to predict.  Sea weeds tend to accumulate iodine, enough so we can use them as a source for industry.  Certain species of a plant commonly called horsetail can accumulate so much silica they become almost as tough as glass.  Fungi are an interesting choice, they tend to absorb heavy metals they encounter in their environment.

What you should do is carefully collect what you need, recording what and where you got it.  Then welhen you use it, you'll be surprised with the result.  This is art, after all. Ash in an inert vessel of some sort unglazed pottery or something like that.

[Joanna_Yle]

Thanks Borek and Arkcon. Really nice of you to answer and share your knowledge!

I understand that it is will be difficult to get some color effect "the natural way" but i would still like to try. Today we can buy ready-made colorants, with all the colors we wish, they are relatively expensive (for example cobolt), but they are reliable and always give consistent results. I don't mind experimenting and getting funny results as long as i don't destroy a kiln.

I read about horsetailash and their high silica content. I must find some and try! I saw in a book (from the potter Miranda Forest) a glaze she made with horsetail ash that was looking red brown - so i suspect it contains iron oxide as well.
I am now processing reed ash (bulrush) and I am eager to see the result!

So fungi is an interesting choice! cool I take it for an encouragement!
The only annoying part is that mushrooms have a high water content... So I need to pick lots of them!

I know that the intake of plants depends of the availability of elements, but we humans, absorb a lot of heavy metals (in the liver) sometimes up to toxic levels. I won't make liver glaze don't get me wrong
So would fungi that grows on ground contaminated with heavy metals have a higher content of heavy metals? (I know that lead and mercury glazes are unstable and toxic when exposed to acid...but they give nice colors! 50 years ago lead glazes were the most common)
In my region there also have been copper mines. So could the fungi here have a higher copper content?

[jasongnome]

Thinking outside the box, one (albeit slow) way you could make it interesting is to "mineralise" some plant matter yourself. Plants will pick up minerals from the soil they're grown in, so if you mixed soluble salts in with soil and grew plants in it you'd get that mineral content in the plant matter when you burned it.

I have no idea how well this would work, nor which plants would work best, and I've never tried it. It's just an idea. Research "phytomining" to see how it's done experimentally and industrially.