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Discolouration of fired white clay products


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#1 Emcarm

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Posted 07 February 2013 - 08:22 PM

Hi,
I have an issue with white ceramic earrings that I am trying to solve. I make and sell white disc form earrings that have a glazed front but an unglazed back surface. I recently saw a couple of customers both who had found that over time their earrings had yellowed. Both customers are friends and have worn their earrings almost daily for a year or so. From what I could tell it seems that perhaps hair oil and products had seeped through the unglazed back of the clay and 'soaked' the whole earring so that the front has also become yellowed.

Has anyone got any ideas of how I could prevent this, save from glazing both sides which would really complicate the way I currently fire them....could you recommend a suitable sealant? Perhaps a metal lacquer that I could apply afterwards?

I would appreciate any of your ideas or experience!

#2 neilestrick

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Posted 07 February 2013 - 08:58 PM

Yep, it's picking up oils and whatnot. HERE
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#3 Iforgot

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Posted 07 February 2013 - 10:35 PM

Perhaps you should coat the earrings with terra sigilatta before the bisque firing. This will make a better seal.



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#4 Lucille Oka

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Posted 08 February 2013 - 04:47 AM

Hi,
I have an issue with white ceramic earrings that I am trying to solve. I make and sell white disc form earrings that have a glazed front but an unglazed back surface. I recently saw a couple of customers both who had found that over time their earrings had yellowed. Both customers are friends and have worn their earrings almost daily for a year or so. From what I could tell it seems that perhaps hair oil and products had seeped through the unglazed back of the clay and 'soaked' the whole earring so that the front has also become yellowed.

Has anyone got any ideas of how I could prevent this, save from glazing both sides which would really complicate the way I currently fire them....could you recommend a suitable sealant? Perhaps a metal lacquer that I could apply afterwards?

I would appreciate any of your ideas or experience!


I used to make ceramic earrings years ago. At first I didn't glaze the backs but I didn't like the look of one side being unglazed so, I started putting one very thin coating of glaze on the backs as well. The stilts that I used did not get embedded into the ceramic pieces and having glaze on two sides makes the earrings easier to clean.




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#5 perkolator

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Posted 08 February 2013 - 12:39 PM

i'd try doing the thin wash like described above, or glaze both sides and fire on bead racks if the holes will allow it.

#6 Ben

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Posted 08 February 2013 - 01:01 PM

Do they have holes? If so glaze the whole thing, front and back and hang them on high temp wires/trees to fire them.
Not seeing them it is hard to give more suggestions. Can you post a picture?

#7 Emcarm

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Posted 09 February 2013 - 09:03 PM

Thanks all for your ideas and suggestions! Because I dont have my own kiln its much easier for me to give the earrings over to someone else to load if they can just be laid flat. Ive thought about bead racks before though the few times I have used kanthal wire Ive had issues with it drooping, though perhaps a ready made rack would be worth investing in. I think the pottery sealant is what Im after at this stage anyway. Attached (hopefully) is a photo for reference.
Thansk again!




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#8 AtomicAxe

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Posted 10 March 2013 - 05:39 PM

I'm assuming you're firing to the 06-04 range ... Pretty much any sealant you use will absorb oils and stains just like porous clay (might extend that time out a little ... but will still happen.) The only way to prevent this is to fire to a vitreous temp, which still might stain as the oils attach to the micro grooves in the clay surface ... or to glaze the piece completely. ... you can fire the earrings like beads on a bead hanger.




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