[nepheline]

I have been working with crackle glazes for a long time but never on fonctional pieces. I have always coloured the cracks with India ink but I know it is not very good for your health. I have tried iron oxyde but it only works on very pale glazes. I have also tried cuttlefish ink but it does not work. Any idea as to what I could use to obtain black lines and not poison my customers ? I would be grateful if someone can help me.

[Mossyrock]

I have used AMACO's black velvet underglaze to highlight the crackle in a glaze. I usually thin it a little, paint it over the crackled glaze, let it dry, then wipe excess off with a damp sponge. I have only used this on vases.....not with pieces that come into contact with food.

This post has been edited by Mossyrock: 15 August 2012 - 04:24 AM

[JBaymore]

Mossyrock, on 13 August 2012 - 04:44 PM, said:

I have used AMACO's black velvet underglaze to highlight the crackle in a glaze. I usually thin it a little, paint it over the crackled glaze, let it dry, then wipe excess off with a damp sponge.

Please note the part of the original poster's question that said "Any idea as to what I could use to obtain black lines and not poison my customers ?"

Have you had these pieces treated this way tested for the potential of getting metal oxides into food stuffs?

The MSDS for these products (which are mighty skimpy on the information I might add) say they do contain metal oxides and "inorganic stains" along with frit, clay, and water and a binder.

I'd personally be interested it KNOW if this is a good practice.

best,

..............john

[Lucille Oka]

Amaco underglazes are formulated to be fired and covered with a lead free clear glaze. Velvet underglazes can be used unglazed but not on surfaces that come in contact with food or drink.

Functional ware or ware that comes in contact with food or drink should not be used with crackle glazes.

If the ware is purely decorative and you still want to stain the crackles you can try strong coffee or tea or a diluted tempera paint, water color, or an acrylic paint but be sure to wipe off the acrylic paint quickly because it dries fast.

[JBaymore]

Lucille Oka, on 13 August 2012 - 06:20 PM, said:

Functional ware or ware that comes in contact with food or drink should not be used with crackle glazes.

Guess I need to hang up the profession. A huge portion of my glazes I TRY to get a good crazing / crackle to develop. Like the image of the Chawan attached below in the current 2012 Kansas City Teabowl National.

best,


.............john

Attached File(s)

•  IMG_6375.JPG (2.95MB)
  Number of downloads: 110

[Lucille Oka]

What's your point?

[Idaho Potter]

I think that Raku--as originally intended--usually ended up with a crackle glaze and the tea bowls were meant to be used in ceremonies to serve teas. However, back then they also used lead based glaze so they could have a low melting point. Did our reluctance to continue using the pottery for food/drink come more from fear of lead or fear of bacteria? I saw a TV program that included ancient tea pots that needed to have tea brewed in them on a regular basis or the pots would disintegrate. It was an episode of Sherlock on PBS so it may have been all fiction--but maybe not. The pots seemed to be unglazed. Is tea the secret sanitizer?

Personally, seeing as teas are made with boiling water, I think that takes care of the bacteria problem. I fire Raku a lot. When sold, there is always a note attached that the vessels are not to be used for food or drink. After saying that, when I make tea bowls, I DO use them for tea--only tea. Not dead yet, but hey, that's what the vessel's intended use.

[bciskepottery]

Nice chawan, John. It is easy to imagine cradling the cup full of tea.

[Idaho Potter]

Nepheline,

Well, shoot! I got sidetracked. If you want the pot to be truly functional, use a non-crackle glaze on the interior, then you only have to test how soon the india ink, or whatever, will last in the dishwashing. I have glazed (to cone 5-6) the interior of a bowl, and then raku fired the exterior expecting crackle. I leave a unglazed band between the cone six and raku glaze (it becomes black during the post-fire reduction). My clay is a raku clay that can take lots of different temperatures. I have also glazed the interior with cone 05-06 glaze which matures during a raku firing. Not knowing what you are firing your work to, makes it hard to adequately address your problem.

Shirley

[nepheline]

Thank you everybody for your answers and suggestions. As Idaho Potter suggests, I should have given you more information about my bowls. They are slip cast with porcelain (so much for raku !!), no glaze on the outside and a beautiful green glaze inside. Looks like a celadon even though it is fired cone 9 oxidation. The cracks lines with india ink are dark, precise, exactly what I am looking for. But India Ink is probably slightly diluted with liquids. Even if it is only a little, I do not want to take the risk. I think the unfired Amaco underglaze is probably just as toxic as India Ink.

Someone here in Switzerland just suggested food colorants. Has anyone tried ?

Thanks for the latin verse but, even though I am french speaking, I'll need a translation. School did not lead me as far as Latin classes.

[DAY]

nepheline, on 13 August 2012 - 11:36 AM, said:

I have been working with crackle glazes for a long time but never on fonctional pieces. I have always coloured the cracks with India ink but I know it is not very good for your health. I have tried iron oxyde but it only works on very pale glazes. I have also tried cuttlefish ink but it does not work. Any idea as to what I could use to obtain black lines and not poison my customers ? I would be grateful if someone can help me.

Just the other day I saw a YouTube video; the Asian artist uses 'india' or 'china' ink, but also uses food coloring for safety.<div>You might google 'india' ink for some formulation info. I suspect it is still- after several millennia- a pretty primitive concoction. Plus, the amount one might &nbsp;ingest is infinitesimal- worry more about the quality of the water used to prepare the food and drink!</div>

[nepheline]

DAY, on 14 August 2012 - 12:42 PM, said:

nepheline, on 13 August 2012 - 11:36 AM, said:

I have been working with crackle glazes for a long time but never on fonctional pieces. I have always coloured the cracks with India ink but I know it is not very good for your health. I have tried iron oxyde but it only works on very pale glazes. I have also tried cuttlefish ink but it does not work. Any idea as to what I could use to obtain black lines and not poison my customers ? I would be grateful if someone can help me.

Just the other day I saw a YouTube video; the Asian artist uses 'india' or 'china' ink, but also uses food coloring for safety.<div>You might google 'india' ink for some formulation info. I suspect it is still- after several millennia- a pretty primitive concoction. Plus, the amount one might &nbsp;ingest is infinitesimal- worry more about the quality of the water used to prepare the food and drink!</div>

[nepheline]

Thanks, I will try the food colouring. But in case someone else is interested I received a suggestion via a teacher here in Geneva : blacken the cracks with a black stain et fire again at "gold" temperature. Sounds like a good suggestion, no ?

[bciskepottery]

You may need to mix some frit (Ferro Frit 3124) with the stain so it melts when refired. 1:1 ratio by volume.

[jo4550]

nepheline, on 15 August 2012 - 04:02 PM, said:

Thanks, I will try the food colouring. But in case someone else is interested I received a suggestion via a teacher here in Geneva : blacken the cracks with a black stain et fire again at "gold" temperature. Sounds like a good suggestion, no ?

Black overglaze aka as China paint/porcelain paint can be mixed with either a waterbased or oil medium and then painted on the warmed pot. Wipe the residue off the glazed surface after it has permeated the craze lines. Fire to 780.c and the black crazing will be permanent. Overglaze is a better choice than black stain as the overglaze is triple roll milled to obtain the very fine consistency necessary for overglaze painting. Overglaze contains its own flux which nowadays has to be lead free in its composition.

Johanna

[scoobydoozie]

Black acrylic paint has always worked for me. Non-toxic and helps seal the cracks. Purchase a high quality artist acrylic and not the 99 cent art store hobby paint. PS - I never use a crackle where it will come in contact with food or drink. Especially when selling a piece, you don't know what the un-informed purchaser will use it for. (as in they may not use it only for tea and use it for something that may allow the cracks to harbor harmful bacteria.)

[JBaymore]

nepheline, on 15 August 2012 - 02:02 AM, said:

Thanks, I will try the food colouring. But in case someone else is interested I received a suggestion via a teacher here in Geneva : blacken the cracks with a black stain et fire again at "gold" temperature. Sounds like a good suggestion, no ?

Sharing a "secret" here that I use........ I use ball milled lead-free china paints and re-fire them.

best,

.......................john



EDIT: Oops... just saw Joanna's posting. Duplicate information. But I take the china paint and ball mill it so that it has an even finer particle size than the originals. Helps it penetrate into the tiny little craze lines.

[blacknapkins]

Tattoo ink. Available in every colour, densely pigmented, pretty cheap, designed to be 'taken internally'. Problem solved!

[JBaymore]

blacknapkins, on 20 August 2012 - 06:34 PM, said:

Tattoo ink. Available in every colour, densely pigmented, pretty cheap, designed to be 'taken internally'. Problem solved!

Just for yucks.. I looked up the MSDS for some Iron Butterfly Tattoo inks. Interesting reading if you know how to read one of those sheets. Notice the N in some categories is not "no issue" it is "not studied".


http://www.tattoopro...s.com/msds.html


Also found this about the inks.... not sure of the validity of the "About.com" source.

http://chemistry.abo...y/aa121602a.htm

Personally, I'll still use a fired product myself on any food contact surfaces that I want to darken the crackles on.

best,

.........................john

[Lucille Oka]

For those who are concerned about their customers this information is from the FDA food code 2009-Cleanability

4-202.11 Food-Contact Surfaces.
The purpose of the requirements for multiuse food-contact surfaces is to ensure that such surfaces are capable of being easily cleaned and accessible for cleaning. Food-contact surfaces that do not meet these requirements provide a potential harbor for foodborne pathogenic organisms. Surfaces which have imperfections such as cracks, chips, or pits allow microorganisms to attach and form biofilms. Once established, these biofilms can release pathogens to food. Biofilms are highly resistant to cleaning and sanitizing efforts.