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billbill

are there any green food safe glazes

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hi

does anyone know of a  green food safe glaze and would share it. they do exist but after weeks ive found nothing. i know there are degrees of "safeness" which is the problem. i spoke with a uk glaze manufacturer who said its acceptable to use a regular green on outside of a mug away from the rim but i would prefer to find one that can be used inside and out

a cafe needs some green coffee mugs and i dont want to be responsible for killing of there customers :)

thanx

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Just use a mason stain for the green color, problem solved. There have been tons of discussions about stains here in the past. It is pretty much decided that the way they are made keeps all the "bad" from getting out, as long as your glaze base is stable in the first place.

http://www.masoncolor.com/stains

Just take your clear and start experimenting with some green stain amounts and it will give you a starting point.

I don't see the issue with copper personally, but I don't want to derail the thread into a safety of copper discussion.

Edited by Joseph Fireborn

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Please provide your firing temperature, and also whether you are firing oxidation or reduction. There are plenty of food safe green glazes. 

There’s another aspect of learning here, which is to never take commercial orders for pots you don’t know how to make yet. It might take a while before you work out all the technical details, and the final product might not be what the customer had in mind. There are too many variables in ceramics to agree on details that were only discussed verbally, without an actual sample in hand. The word “green” alone can mean so many things! 

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Copper can generally be used safely in amounts of 4% or lower. Testing required, of course. There are also iron greens, mason stains, etc. Lots of ways to make safe green glazes. If you have a good safe clear or white glaze, it should be safe to use with any of those additions to make green as long as you don't overload it with coloring oxides.

In addition to all the other info that has been requested, what shade of green do you want?

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hi

thanks everyone , would have been back sooner but am not getting notifications. will check frequently

will be stoneware temps about 1260c

mid green probably . does darker mean more copper?

oxidization.

i could use mason stains but would prefer to make a glaze [i will check the m/stains link, thanx.

right now i want to do some samples, not the actual order

Neil: what is iron green pls. ive got a few iron oxides here, i also have a good clear base glaze

 

thanxs

Edited by billbill

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It takes a relatively small amount of mason stain (a powder) added to your base glaze for colorant and the color is generally more consistent and controllable than oxides. Do you want a dark green, like forest? There's a stain for that. 

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2 hours ago, Rae Reich said:

It takes a relatively small amount of mason stain (a powder) added to your base glaze for colorant and the color is generally more consistent and controllable than oxides. Do you want a dark green, like forest? There's a stain for that. 

thats interesting . a mid green , i will look in my boxes and see what ive got.....what are masons stains? there site was no help

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2 hours ago, billbill said:

what are masons stains?

Mason stains are powders that can be added to paints, clay, cement, etc. that add color.  They are made up of different elemental combinations that are calcined or encapsulated so that the colors are quite stable and safe for use.  For ceramics, they are used as glaze colorants or clay body colorants (best if using a body stain specifically for bodies).

See the Mason Color web page for ceramic stains for more information.  Many of these are carried by many ceramic suppliers, like the one Rae Reich posted while I typed this.

Others include The Ceramic Shop, Sheffield Pottery, and US Pigment Corporation.  There are hundreds of possibilities.  Search for the one with the best price for your location.

Edited by Soren
Added additional links

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2 hours ago, billbill said:

what are masons stains?

Mason is a manufacturer of ceramic stains, originally founded in Stoke-on-Trent in the UK but moved to the US in 1902. Depending on where you live it might be Mason stains that are available or could be Potterycrafts or another supplier.

An explanation of what stains are here.

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thanks to several people above.

i looked in my box and found other color stains , if i cant find a food safe  green glaze to make i will order masons stain in green. now that i know what it is Soren.

am in uk. interesting that masons moved to the US, always thought they were American. couldnt find any ref to  that green iron [as above] on the web

ive got lots of raw  glaze ingredients and have vowed to use them before starting something new like stains, unless i have no alternative

thanx

Edited by billbill

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if your final glaze coat contains zinc, the green may change to grey.  get all the info about what is in the stain you use, most mason stains use  chromium which reacts with zinc badly.   zinc can be found in glazes even if the name "Zinc" does not appear in the recipe.  

 there are lots of green mason stains, i have tested many of them and have not gotten a satisfactory green from them.  perhaps you can convince the client to use  a white interior so users can easily judge the contents and cleanliness of the mugs by looking inside.

Edited by oldlady
spell

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Iron greens, as I remember, are celadons. Glazes with a small amount of iron, fired in reduction. Traditionally, high-fire and reduction on porcelain is the standard for aesthetic appreciation. Celedons, from pale greens and blues to darker, olive-like as @neilestrick says, can now be approximated for lower temps and even without reduction, if you're not a purist who needs to do things the older, more difficult and years to learn way.

So, for food safe medium greens, look for celedons.

Edited by Rae Reich

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interesting about the zince [none here] i intend to use clear made of:

calcium borate  40

lead biscilicate 35

cornish stone 10

china clay 5

whiting 10

so it seems [from above advice] that to this is can add iron to make green which is a celedon...right?

i dont see anything toxic here,  if i make it, the lead is fritted and i think iron is ok. would this glaze be safe? am i right to think that this celedon can be modified/made for s/ware in oxidization?

thanx

 

 

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5 hours ago, billbill said:

would this glaze be safe?

No.

The glaze is going to leach. To make a stable glaze you need to have minimum amounts of both silica and alumina. This glaze is very low in both of these which will result in leaching. 

Lead, many discussions on this forum talking about the very real hazards of lead, one of them here

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On 9/1/2018 at 12:01 PM, neilestrick said:

No good reason to use lead, especially at high temps.

You should be able to Google search a nice simple clear base glaze that works at cone 9, and add a green mason stain to get the color you want.

This.

You will not be able to get an iron green celadon in oxidation. That's why you will need a stain to get the color you want.

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I didnt do the math for 1260C, but I have never heard of green glazes being not food safe. I fire to cone 5/6 and have regularly used green glazes. One combo is cerulean on the bottom layer and celadon froth on top - but it’s runny. Some other choices are Amaco Potter’s Choice and Celadons. A nice combo is Rainforest down with Textured Turquoise above and Rainforest down with Oatmeal above.

There is a group on Facebook called Amaco cone 5/6 where people share their combinations and tests. They are very nice and generous. 

Good luck!

nancy

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Not to be a downer but it might be a little optimistic to make a glaze from scratch and have it come out as you expected without lots of experimenting, and for it to be strong, safe and not craze down the line. Especially if its going to be used in a cafe, man handled, washed multiple times per day with harsh cleaning products, put in a dishwasher and microwave etc.

I'd also be MUCH more concerned that you were going to use lead in a glaze than a bit of copper oxide or chromium, or that the base you picked is for a low/mid firing temp range when you're talking about high firing. If you are selling your wares its your responsibility to understand the chemistry and risks...

I'd probably recommend buying a commercial glaze for the time being (not that that's a guarantee for a well formulated glaze, but go with the big brands), then get a couple of books on glaze making. John Britt's - The Complete Guide to High Fire Glazes is a very good starting point, and Linda Bloomfield - Colour In Glazes has plenty of greens and blues in. (And if you really get into it ceramics material workshop does some amazing online glaze chemistry courses)

Edited by MartinB

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