Help colored slip turned black

[VForce]

I just mixed a bunch of colored slips for the studio using trimmings from Laguna #65. I left the studio for 2 weeks and I come back and all the slips I mixed have turned black and smell something fierce. How can I fix or prevent this for next time cause I definitely just burned $20 of mason stain. Would a vinegar ratio have killed bacteria growth? Should I not have used trimmings and just mixed a clay base?

[Benzine]

You've just got a bit of fungal, or bacterial growth.  Based on the smell, I'm guessing bacterial.

I believe that some potters add a small amount of copper carbonate to their slips and stains, to prevent growth.  Someone will be able to chime in, and give you a better idea.

However, your slips will still fire to the correct color, in the kiln.  The black color is organic material, and will burn out.  Unless of course, there is a bacteria or fungus, that can withstand kiln temps... Then God help us all!

[oldlady]

try adding some clorox and stirring it well.   i have slips that i made over 25 years ago and sometimes it needs cleaning up.

[Brandon Franks]

2 hours ago, VForce said:

I just mixed a bunch of colored slips for the studio using trimmings from Laguna #65. I left the studio for 2 weeks and I come back and all the slips I mixed have turned black and smell something fierce. How can I fix or prevent this for next time cause I definitely just burned $20 of mason stain. Would a vinegar ratio have killed bacteria growth? Should I not have used trimmings and just mixed a clay base?

I make my colored slips using oxides.

 

Example, my blue slip is 97.5% Porcelain and 2.5% Cob. Carb. 

Black/dark red is 75% RIO, 25% Brown/red clay.

 

I hav found these to last longer then mason stain slips and produce better colors. You can alter colors by adding different oxides.  I also put small amounts of Sodium Silicate, (Any deflocculant should work,) in my slips, I find that the PH reduces the amount of bacterial growth. It's all about what works best for you.

Now, for your issue. You are probably storing your slips in a container that isn't 100% sealed. Mason jars always work best for me. I have never had an issue with evaporation or slips going bad. Try glass or thick plastic containers with airtight lids.

 

Try to fire them, they might come out the correct color, just be the wrong color before fired?

[Callie Beller Diesel]

A shot of peroxide will also work, if you dislike the notion of using bleach. A little mould won't hurt the slips: stains are stable at room temperature. However the stink is no fun, and if it's bad enough you can't see the colour, that's a problem.

I don't think the mould is a result of a sealed or unsealed container necessarially. Reclaimed clay can have extra things like dead skin cells and whatever else that can make excellent growing medium, or if there was anything in the container to start with like a tiny trace of yogurt.

 

[VForce]

Thank you all so so much!!! Way way way more information then I was expecting and so fast, ceramic Lifesavers all of you! 

I'll let you know if the bacteria survives the firing so we can all start building our bunkers

[Benzine]

22 hours ago, Callie Beller Diesel said:

I don't think the mould is a result of a sealed or unsealed container necessarially. Reclaimed clay can have extra things like dead skin cells and whatever else that can make excellent growing medium, or if there was anything in the container to start with like a tiny trace of yogurt.

 

Yes indeed.  Which is why I tell the students the slip bucket, and reclaim bin (especially the lower, undisturbed portions of it) always smell FANTASTIC.  

They usually forget this fact, and it's fun seeing their faces, when the smell hits them.  

Even the commercial underglazes I get, sometimes develop said "Funk".  I also warn the students about this.  Usually you can have a good idea, which colors will smell, because you can actually see black in the jar.  Once again, they sometimes forget, that I mentioned it, and shortly later, the entire room remembers.  I don't even need to see that someone is using an underglaze, because either I smell it from across the room, or I hear the reaction from everyone else...  Good times!