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Black/Grey glaze food safety


Gonepotty

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Hi all, quite new to the pottery scene and learning every day. I would like my my own glazes rather than purchasing commercially available glazes. Question I have is regarding black&grey glazes....most recipes I have come across contain manganese which I know is toxic so can't be used for tableware nor do I want to be using it in my studio. I have seen some potters with the most beautiful black and grey glazes on tableware items (ie mugs and bowls) but am scratching my head as to how they achieve this considering the toxic nature of manganese. Are they using a black stain?? I don't know much about using stains but wondering if this is something that gets added to per say a white base glaze recipe? Any thoughts or tips would be most appreciated. Thanks:)

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4 hours ago, Bill Kielb said:

Quite a few ways to do this including underglaze and stain. Can you post a picture of something you like?

Thanks Bill, I have today experimented with a black slip on greenware but will know the result once bisque fired- I'm assuming it won't be that black but more of a darker grey.  Didn't think of using an underglaze so thanks very much for this info:) Would it be best to use a black underglaze and then perhaps apply a clear/satin/matt glaze?

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4 hours ago, GEP said:

Mason Satin Black 6600 does not contain Manganese. It is Chrome, Iron, Cobalt, Nickel. and makes nice grays and blacks. 

This is really brilliant news and was wondering how to get different shades of black and greys.  Can Mason stains be added to any base recipe? For example a  clearor white gloss/satin/matt? 

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8 hours ago, Gonepotty said:

I have come across contain manganese which I know is toxic so can't be used for tableware nor do I want to be using it in my studio

Going to back this conversation up a bit. Manganese is not a problem through skin contact and not a problem through ingestion so the dinner ware is not a concern. Where manganese is a hazard to the potter is through the fumes. I don't want to overwhelm you but if you want a clear explanation of the risks associated with glaze safety grab a cup of tea and have a look at the video below. This is an excellent overview of glaze colourants etc, if you prefer to read then this link has a condensed version of much that is covered in that video. Manganese folklore is discussed on page 9.

I would be more concerned about copper in a black stain than manganese. I did a quick look for a black stain in England, this one, Carbon Black, from Potclays came up. If you scroll down you can see it contains copper, iron and chromium. Copper is much harder to keep from leaching out of a glaze than manganese.

Having a durable non leaching base glaze like @kswan linked to is really important. Get the base glaze sorted out then test with stain. The composition of the base glaze will have an effect on how the stain turns out. Mason Stain has a reference chart showing the parameters each stain works best under. For Mason Best Black 6600 for example the chart indicates it can be used as a glaze or body stain, max temp 1260C and it can be used with or without zinc in the glaze.  Some stains aren't fussy about the base glaze they go in, others can look drastically different in a non compatible base glaze. 

It's also possible to make a good black with just iron oxide and cobalt. At cone 6 Licorice black is a good example of this.

 

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(Where manganese is a hazard to the potter is through the fumes.) Thanks Min for adding this as many are so afraid of maganese and its fine except for the off gassing thats why wielders have issues as it in the fumes. With a good vented kiln to the outside its really a non issue

 

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3 hours ago, Gonepotty said:

This is really brilliant news and was wondering how to get different shades of black and greys.  Can Mason stains be added to any base recipe? For example a  clearor white gloss/satin/matt? 

As others have mentioned, if you’re making foodware make sure the base recipe is durable, non-leaching, and a good fit for your clay. But yes, Black 6600 plays will with others. Combine in tiny amounts with a white opacifier to make shades of gray. 

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