recycled clay and mold

[Half Baked Ceramics]

Hello all, I have been recycling clay for many years now and I have come across an issue I have not seen an answer for.  My recycled clay looks fine from the outside but when I cut a piece of it off the entire inside is black.  There is a border of about 1/2" where the clay looks fine, but the inside is all black.  When I use this clay it smells really bad.  The clay itself is fine and it does not really affect the throwabliity of the clay and it fires fine.  I also have a slop bucket and I try to put vinegar in the bucket but after a while it goes back to smelling badly.  I am guessing I have to throughly mix the slop bucket with vinegar to eliminate the smell.  I guess my question has to do with the first part of the clay being black on the inside, why does it only get black on the inside and how do I get rid of black part and the smell short of throwing it away?  I also do not want to use bleach.      Thanks

[Kelly in AK]

My guess is that the clay has a lot of organic material in it. Anaerobic bacteria, explains the clear rind, the depth oxygen can penetrate. My experience : When paper towels get in the slop bucket it makes a black zone. Perhaps the clay you use has an organic plasticizer added. It would be worth checking (with your seller), because it sounds like the whole batch, not just pockets are reacting.

 I have no solution though, just a possible “why.” 

[PeterH]

Potentially relevant?
 

 

[JohnnyK]

Interestingly enough, I was acquainted with a production potter about a decade ago that was visiting a friend and we got together at the friend's home and threw some pots. I had mentioned that I had some reclaimed clay that had gone green on me, and he chuckled and said that he felt that the mold gave the clay character, and I shouldn't have any problem using it. What I did find, if I can recall correctly, was that when I wedged and fired the clay, some of the pots had a swirly, agate look to them, and the green burned off, but the integrity of the clay remained...

[Min]

15 hours ago, Half Baked Ceramics said:

but the inside is all black.  When I use this clay it smells really bad

Yeah, solid black mold in the clay is really rank! If you stir hydrogen peroxide (like in Peter's link) into scrap clay that has been slurried down into slip it will kill the black mold. Keep stirring and adding hydrogen peroxide until the black colour is gone then let the bucket sit for a few days then dry out the reclaim with your usual method. (the hydrogen peroxide will revert to water) If you look for "natural bleach" in the cleaning aisle of larger grocery stores and check the label that it is just hydrogen peroxide it will be less expensive than buying the little bottles of it from a pharmacy. 

[Callie Beller Diesel]

Be careful not to use oxy-clean or others like it! They’ve got extra surfactants and sometimes soda ash that will make a mess of your clay.