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Chris Campbell

Glazed Piece Fading In Dishwasher

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Here is a link to my Facebook Color/Colour in Clay page ...

 

https://www.facebook.com/groups/286531511532039/

 

The first post with pictures is from a newbie who is noticing significant fading on a colored clay glazed piece that has been run through the dishwasher several times.

 

Any comments would be welcome as this is a new problem for me.

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It's hard to tell from the image, but I agree, it looks a bit like hard water and detergent deposits. Is it rough to the feel? Does a little vinegar or CLR take it off?

Solubility of glaze wouldn't be my first thought with this example, because the "fading" looks like it's on the unglazed back as well as the glazed front. Cone ten porcelain shouldn't fade like that just with water, like blue jeans in the wash. There's too much glass content, even with colourant added.

 

How long has the piece been going through the dishwasher like that?

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At first I didn't think glass could fade, but then I remembered the field archaeology classes.  In burials we would

find black/navy blue, white, and red glass trade beads.  The red beads and only the red beads were leached out and

the outer layers flaked off.  Almost all the red was gone.  So I think red glass whether it's a glaze or glass bead can

leach out or decompose.  We found most of the beads and other small items while in the sorting process inside the

lab when it was raining or in the off season.

     I have been just able to go to the face book images.  It appears to be in the clear glaze..  if you could find out the

glaze recipe, then another forum member might be able to tell you what the problem ingredient is.  Until the problem

is found, I'd handwash them, and take more photos as a record.

See ya,

Alabama

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Guest JBaymore

From the photo the backs sides on all of those look about the same to me.  But the center piece on the left side image on the glazed side DOES look etched.  Doesn't seem to be the clay body....... but the glaze to me.  But pictures like this are REALLY hard to tell.

 

Get the glaze recipe and put it thru Insight (or other glaze calc software).  First guess....... undersupplied with SiO2.  Or has Boron.  Or high alkaline flux content.

 

best,

 

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

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The potter has tried scrubbing with various products ... No change. She covered the surface with black marker then wiped it, but no easily visible crazing.

New pix posted today really show that not only are the pieces fading, but the black is changing to blue which indicates some type of leaching.

I'm still suspicious of the glaze ... It just cannot be fitting properly if it is letting the chemicals through. She will post the recipe when she can contact the person at her arts center who mixes them.

All ideas welcome.

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Guest JBaymore

Chris,

 

I looked at the new pictures....... better images... and shows the issue much better.  If the unglazed CLAY on the backside is not also changing color like this, then it is for sure the glaze that is not standing up to the chemical environment and the abrasion of the dishwasher.  Which it is technically POSSIBLE for a stained clay body to also lose materials from the outer surface... it is less likely.

 

At high fire (like cone 9-10) the glaze /body interface layer (not glaze/not body) is picking up the coloring oxides from the underlying clay and those colors (and other materials from the body) are becoming part of the glaze.  So if the glaze itself is not stable, then it allows some of those materials to be affected by the change in the glaze.

 

I think the "lightening" of the colors (not the significant color change) and the loss of shine is the fact that the glaze's surface is becoming "etched" as the surface is both slightly dissolved by the strong Ph change of the dishwasher detergent in the very hot water, plus the "sandblasting" effect that is a part of the dishwasher's process with the detergent. 

 

In any case... it is an issue for functional stuff from both a "repeat customer" standpoint... and potentially also a toxicological one.

 

best,

 

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

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I agree John ... I don't put my own work through the dishwasher so I had no info for her, but I believe the glaze firing is the culprit ... and now she writes it was fired in an open studio setting with less than optimal control over the firing process. Large mixed loads in a car kiln with efforts to try to hit Cone 9 throughout ..."but doesn't always make it".

I certainly have a lot of other people's pottery that does go into the dishwasher every day and none of it is faded or cloudy looking.

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