Blue Green leaching on french butter dish?

[Simon Heath]

Hi there,

People have been so helpful in the past, I wonder if I could ask for some more help.  I have a french butter dish that I made with bright white porcelain (porcelaineous) with simple clear 5/20 glaze.  I fired the two pieces separately as I was worried they would fuse together.  This means, there is an unglazed rim on the interior piece, which is exposed to the water (but not the butter).  That unglazed rim has developed a weird blue green colour (as seen in photo).  Does anyone have any idea what this is?  It's fired to cone 6 and I would have thought vitrified the clay.  Could it be from the water?  Any thoughts appreciated!

Simon

[neilestrick]

My guess is it's some sort of mold. Not at all uncommon in French butter dishes.

[Min]

Salted butter or unsalted? Makes a difference in how fast it turns. 

[Jeff Longtin]

A simple way to find out if its your water...go into the bathroom and lift the lid on the toilet tank. More than likely the tank has a ring of some color. (Brown means you have iron in your water and blue green means you have something else?) 

If the tank water ring matches your butter dish ring I would presume its just a water issue. (Minerals in the water in other words.)

[Bill Kielb]

My guess - blue mold, butter is a dairy product and usually goes rancid before you can see the mold. It does mold though. Blue - Blue Green common.

”Blue mold or bluish-green mold in the home is usually one of two types of mold, Penicillium or Aspergillus. They are some of the fastest growing molds (usually within 24 to 48 hours) and require very little moisture for their colonies to develop.”

[Callie Beller Diesel]

As far as a clay being vitrified at cone 6, it depends on the clay you were using. A clay body that is sold as a cone 6-10 clay will be a lot more porous when fired at cone 6 than it is at cone 10. For food dishes, I find it’s best to aim for your porosity to be less than 1%. Even if your clay body is a true midfire clay, it’s always a good idea to do a porosity test to confirm against manufacturer’s specs. Your method of firing may be different than what the manufacturer used to supply that info.

The colour seems unusually vivid for mould growth, and usually there’s other colours involved as well. What it cleans off with will possibly also give you more info. 

If it cleans off with hot soapy water, bleach or peroxide, that would indicate bacteria of some kind. Or maybe something it picked up from the counter? I have kids, so my mind goes to something like drink mix, or dye transfer from some kind of wet packaging. 

If you need something like vinegar or CLR to remove it, that would mean it’s probably from the water.

[Min]

Going forward if you want to glaze the rim of the lid you can wax the rim of the water crock plus the area under the top of the lid and fire them together. When I do this I also wax a little ways down the tube of the lid. Have to have a really well fitting lid to do this the parts don't fuse together when glaze firing, tapering the tube part helps with this.  Image below is from this article by  Sumi von Dassow , she glazes them the same way you did, I added the red arrows to show an alternate way to wax and fire them.

[Simon Heath]

18 hours ago, Callie Beller Diesel said:

As far as a clay being vitrified at cone 6, it depends on the clay you were using. A clay body that is sold as a cone 6-10 clay will be a lot more porous when fired at cone 6 than it is at cone 10. For food dishes, I find it’s best to aim for your porosity to be less than 1%. Even if your clay body is a true midfire clay, it’s always a good idea to do a porosity test to confirm against manufacturer’s specs. Your method of firing may be different than what the manufacturer used to supply that info.

The colour seems unusually vivid for mould growth, and usually there’s other colours involved as well. What it cleans off with will possibly also give you more info. 

If it cleans off with hot soapy water, bleach or peroxide, that would indicate bacteria of some kind. Or maybe something it picked up from the counter? I have kids, so my mind goes to something like drink mix, or dye transfer from some kind of wet packaging. 

If you need something like vinegar or CLR to remove it, that would mean it’s probably from the water.

Thank you - I agree that I don't think it's mould.  Odd colour, and not on the butter at all, just the unglazed part exposed to water.  The stated porosity is 1% at cone 6 and I tend to fire high, more like a cone 7 (the cone 7 cone is always completely bent over).  Will try CLR.

S.

[Simon Heath]

18 hours ago, Min said:

Going forward if you want to glaze the rim of the lid you can wax the rim of the water crock plus the area under the top of the lid and fire them together. When I do this I also wax a little ways down the tube of the lid. Have to have a really well fitting lid to do this the parts don't fuse together when glaze firing, tapering the tube part helps with this.  Image below is from this article by  Sumi von Dassow , she glazes them the same way you did, I added the red arrows to show an alternate way to wax and fire them.

Thank you, yes, ultimately this is how I would like to do it, but the fit on the last few I've thrown has been too snug to do this.   I think this is how I will have to do it going forward.

S.

[Min]

1 hour ago, Simon Heath said:

Thank you, yes, ultimately this is how I would like to do it, but the fit on the last few I've thrown has been too snug to do this.   I think this is how I will have to do it going forward.

S.

If you want a "cheat" to help stop them sticking together during firing there is a workaround. Use a different clay, ideally a cone 10 body, and fire a holder for the lids. Make it like the shape below with the straight tiny wall at the top only about 1/2cm high, since this lid holder will be reused make it from clay that can take multiple firings without bloating etc. Raku clay or a cone 10 stoneware are good choices. Bisque it then use that to fire the lids on instead of with the crock part.

[Simon Heath]

12 minutes ago, Min said:

If you want a "cheat" to help stop them sticking together during firing there is a workaround. Use a different clay, ideally a cone 10 body, and fire a holder for the lids. Make it like the shape below with the straight tiny wall at the top only about 1/2cm high, since this lid holder will be reused make it from clay that can take multiple firings without bloating etc. Raku clay or a cone 10 stoneware are good choices. Bisque it then use that to fire the lids on instead of with the crock part.

Clever.  Thank you!

[Mark C.]

Been in the french butter business for over 40 years and most folks do not wash them out and start over enough. Leads to many issues. Remember its not a long term storage container. Wash it out at least every few weeks.

We personaly use a covered butterdish ona plate bottoms as it easier to keep clean .

Most customers go sideways with these items and ask about how to use them later although I have detailed instructions in each pot I sell.