Georgie's Cone 6 Trailmix leaching water, mildew issues

[CupCupStudios]

Hey All,

I've made a ton of stuff with Georgies Cone 6 Trailmix (white) stoneware.  I recently noticed dark coloring (mildew) on a lot of my pieces.  Similarly, I've noticed the pieces I have glazed with Vanilla Cream Matte are leaching water.  I let a cup of water sit overnight with a paper tower underneath, and sure enough, the paper towel is wet.  I did a similar test with a glossy glaze, and that towel stayed dry.  However, the bottom of that mug is still showing signs of discoloration.  I attached a photo in which the top mug is unused from the kiln, and the rest are clearly discolored. 

I think my clay isn't fully vitrified, even thought I fired it to Cone 6.  I use a Skutt electric kiln, but sadly I started getting lazy and not putting my witness cones in.  I'm running a firing right now to test the kiln with witness cones on all three layers.  

Can I and should I refire these pieces to a Cone 7?  I'm concerned I'll start to see glaze issues.  

For future pieces with this clay body and glaze combo, should I use a liner glaze to avoid the leaching?  Any advice on what liner glaze to use?

I really appreciate your help - I have my first pottery fair in three weeks and I'm in a bit of a tizzy

 

[Benzine]

Clay mold won't hurt a thing, unless you happen to be allergic to it.  It just means it's aging nicely.

 

If it is weeping , then you definitely have an unvitrified, underfired Cone 6 body. 

Your witness cones will tell the tale.  What kind of controller are you using?

[Min]

14 minutes ago, CupCupStudios said:

I think my clay isn't fully vitrified, even thought I fired it to Cone 6

Agreed! Trail Mix original has a posted absorption of 3.5% at cone 6 so even if you did fire to cone 6 it isn't going to be vitrified. It matures at that cone but it's not vitrified. The 3.5% is their posted figure but you really need to run your own absorption tests to see what it is with your kiln and your firing methods. You could try firing to cone 7 to see if the clay tightens up enough but it might be better in the long run to switch to a clay with a lower absorption, under 1 1/2 to maybe 2% but again, test it before making a lot of work. 

 

[liambesaw]

20 minutes ago, Benzine said:

Clay mold won't hurt a thing, unless you happen to be allergic to it.  It just means it's aging nicely.

 

If it is weeping , then you definitely have an unvitrified, underfired Cone 6 body. 

Your witness cones will tell the tale.  What kind of controller are you using?

He means mold on his fired pieces, you can see the mildew he's talking about on the bottoms of his feet there.  No bueno

[Benzine]

7 minutes ago, liambesaw said:

He means mold on his fired pieces, you can see the mildew he's talking about on the bottoms of his feet there.  No bueno

You don't take mold in your coffee?

[liambesaw]

5 minutes ago, Benzine said:

You don't take mold in your coffee?

Only on Tuesdays 

[CupCupStudios]

Thanks all - Since then I ran a bisque fire with witness cones to 04 and saw only a very slight bend in the cone, indicating my kiln is running a little cool.  This is only my 14th firing on a brand new kiln, so I'm still learning how it works!  I use a Skutt electric kiln with a kiln sitter.  

Based on advice I saw on another post, I refired a lot of these mildewed pieces to cone 6 again to burn out the mildew.  Additionally, I soaked for 12 minutes, and my cone 6 cones were PERFECTLY bent    The mold is gone and now I'm conducting more tests to see if water is still leaching through - I'll update you soon.  

In the meanwhile, it's great to know a little more about my kiln.  If at this point the water is still leaching, I will absolutely be changing clay bodies.  I find it very odd that Georgie's "Most popular clay!" is so porous!  In my opinion, a clay that leaches by nature should not be advertised as a sort-of 'everyon'es clay body'.  

Thanks very much for the advice and I'll keep you posted.

[oldlady]

if you are using a matte glaze inside, you might re-think it.  first, it is hard to clean enough so it LOOKS clean.     when you tested with water and paper towel it failed.  yes, i know it is the clay but even if you change clays, i would bet the matte glaze will still weep.   shiny inside and matte outside if you want but not matte inside.    

advertising  shows so many impossible things you cannot believe anything except that someone wants your money.    (remember the scrubbing bubbles?  my children cried for hours when there weren't any.)

[Min]

1 hour ago, oldlady said:

when you tested with water and paper towel it failed.  yes, i know it is the clay but even if you change clays, i would bet the matte glaze will still weep.   shiny inside and matte outside if you want but not matte inside.

Pots for functional work like mugs, vases etc shouldn't leak even with no glaze inside or out. Having a matte glaze inside might have aesthetic issues but it won't make a difference to weeping pots in regards to leaking if the clay is tight.

[CupCupStudios]

29 minutes ago, Min said:

Pots for functional work like mugs, vases etc shouldn't leak even with no glaze inside or out. Having a matte glaze inside might have aesthetic issues but it won't make a difference to weeping pots in regards to leaking if the clay is tight.

This is my thought exactly.  As an update, the mug with vanilla cream matte still weeps or leaks or whatever you want to call it.  I left it filled with water overnight on a dry paper towel, and sure enough the towel had substantial amount of water on it this morning.  My hypothesis is that even when fired up to a true cone 6, these pieces will probably mildew again if given enough time.  My thought is that if water can simply pass through the body of the mug, it will retain that moisture and cause mildewing. 

With that in mind, I am definitely going to stop using this clay body and seek something with a lower absorption.   Per oldlady's advice, I'm also going to investigate liner glazes for the inside of these mugs to ensure they stay nice and clean for a lifetime.  I'm going to search for a thread on that now and create one if I can't find it. 

I am so thankful for your time and expertise, everyone!  

[Deleted user]

Done with this forum

[liambesaw]

Trail mix according to Georgie's website has an absorption of 3.5% it's one of their least vitreous clays.  The only midrange clay worse is their g-mix with grog at a whopping 8.9%!!!  Yikes.

[Deleted user]

Done with this forum

[liambesaw]

I use a high iron body and when fired in reduction all of that iron seals it up tight.  If you like the white stones there are plenty to choose from, I think the 2% and less are fine for functional ware.  If you are using a liner glaze that fits your body really well it doesn't really matter as much since that layer of glaze will help keep liquids out of your clay

[CupCupStudios]

1 hour ago, liambesaw said:

Trail mix according to Georgie's website has an absorption of 3.5% it's one of their least vitreous clays.  The only midrange clay worse is their g-mix with grog at a whopping 8.9%!!!  Yikes.

I was trying to find that info - thank you!  8.9% is crazy - sounds like it's probably intended for sculptural work, yeah?

[Min]

2 hours ago, liambesaw said:

If you are using a liner glaze that fits your body really well it doesn't really matter as much since that layer of glaze will help keep liquids out of your clay

With all due respect I disagree. The glaze shouldn't be relied upon to seal the clay. 

[Magnolia Mud Research]

Been reading the Bernard Leach's book this week.  His solution was to use a slip that matured at the firing temperature to 'seal' the earthen ware his pottery produced.  

 

[glazenerd]

Functional use: absorption is 2% or under. Absorption is tested unglazed. 

Modifying LT's suggestion to this specific purpose would work. Make a slurry out of the current clay: add 5% frit and 5% Nep Sy: apply as a slip. Should put you at 2% or under at C6. Then you have a functional body with the clay and cone you are use to.

T

[liambesaw]

4 hours ago, Min said:

With all due respect I disagree. The glaze shouldn't be relied upon to seal the clay. 

Oh I disagree too, just saying that a well fitting liner glaze may help in the current situation.  I wouldn't rely on it long term, it's just a bandaid

[CupCupStudios]

8 hours ago, liambesaw said:

I use a high iron body and when fired in reduction all of that iron seals it up tight.  If you like the white stones there are plenty to choose from, I think the 2% and less are fine for functional ware.  If you are using a liner glaze that fits your body really well it doesn't really matter as much since that layer of glaze will help keep liquids out of your clay

That makes sense re: liner glaze.  The other thing I'm thinking about though is the mildew.  Do you think the mildew is a direct result of the high porosity of that clay body, or was that due to having probably not fired it to true cone 6?  Or perhaps something else entirely?  Only time will tell if the mildew comes back. 

[Mark C.]

Trailmix clay that sound goods for backpack trips as well.Sounds pretty tasty with some vanilla cream Matte poured over it-maybe roasted on a stick on the campfire.Gotta love Gorgie's for these hobbyist names that appeal to hunger.Maybe they they have a room of Madmen working for them???

[liambesaw]

8 minutes ago, CupCupStudios said:

That makes sense re: liner glaze.  The other thing I'm thinking about though is the mildew.  Do you think the mildew is a direct result of the high porosity of that clay body, or was that due to having probably not fired it to true cone 6?  Or perhaps something else entirely?  Only time will tell if the mildew comes back. 

It's porosity + time.  If you wash and dry it and it doesn't sit wet for long you should be fine.  But if you use it a lot and it's always wet, you'll get the mildew back pretty quick.  If it was vitrified the water wouldn't penetrate and there wouldn't be much of a spot for organisms to cozy into.