Glaze Disaster

[Thrown_In_Stone]

Well, I seem to have found one of my famous explosive glaze combinations again.
 
I have 2 glazes (Blue and white) The blue is fabulous, it's never let me down but I tried putting a white over the top of it this time and OH MY DEAR GOODNESS. I attach a picture of the the result in in the kiln and one of the pots.
 
The glaze doesn't seem to have run off the pot, more fallen off; I just don't know at what point during the firing though.
 
The recipe for the white is: 
 
Calcium Borate Frit:   39
Soda Feldspar:           27
Whiting:                       5
China Clay:                 6
Quartz:                      23
 
Zirconium Silicate:    10
 
Cone 04.
 
 
Any ideas? Is there ingredient that may be in the Blue glaze that the zirconium it's reacting badly with?

[mregecko]

Huh, interesting. It's almost like the surface tension was affecting to the point where it beads up and falls off. I actually almost like the spotted effect on the photo of the vase.

 

The photo of the bottom of the kiln is a bit hard to see, but the thing that strikes me is the DISTANCE from the pieces the glaze is. Almost like shards that pinged off.

 

I'm not an expert at glaze chemistry, so I'll defer to other on the mechanics of what happened. But given the distance and the shape of the glaze on your piece, this is a weird one.

[Chris Campbell]

OUCH!!! Looks like the glaze spit off ... or flung itself off ... weird.

The most amazing part is that those white mugs didn't get splashed as well.

[Min]

Maybe post the blue glaze recipe also since the white alone on the mugs looks great.

[Kohaku]

The jar is actually quite interesting- surface like scales on a carp. That would be a wonderful effect if it could be controlled...

[Thrown_In_Stone]

Thanks for your comments.

 

I actually like the vase too, In fact  it's in my kitchen filled with water to test if it leaks (being earthenware), If it doesn't I'll be selling it or at least using it for myself, looks like it should have come out like that!

 

I should note that I wasn't best pleased as this is my brand new Skutt kiln; 3rd firing ever (fist glaze firing). However I know this isn't the kilns fault as it did it in my old one once, not quite the same glaze combo but almost the same. Thankfully not too much damage to the kiln, most of the glaze came off the batt wash with only minor grinding needed. Also ran off the shelf onto the bottom slab which after removal left a 1cm deep hole in one of the bricks *SOB* . Though I'm extremely thankful that it wasn't worse, as one of the splashes was 15mm away from the bottom element groove (how lucky am I?).

 

The glaze in the mugs is not the white, it's transparent but almost identical base glaze.

 

I'll try find the recipe for the blue and post it later.

[bciskepottery]

Colemanite Splutter.  A glaze with a large amount of colemanite (e.g., calcium borate frit, gertsley borate, colemanite) can cause the type of ejection in your photos. 

[Babs]

Hi I likes the glaze too but was very empathetic re new kiln... bright side, no element damage!

I used a glaze by Emmanuel Cooper which had similar characteristics when thick i.e. spat out from pot. the colouring additive for that glaze was Nickel , The glaze gave a great blue/shocking pink colour, but unlike yours , was fired to C9.

Was your colourant Nickel?

here's the recipe for those who like trials

Shocking Pink Glaze Emmanuel Cooper

Feldspar        35

Barium Carb. 40

Zinc Oxide     15

China Clay       5

Flint                  5

 

Add

Nickel Oxide      1.5%

Great colour.

[Mart]

Someone told me, if glaze is still wet and thikc, it will be fying off the pott, if temp is rising fast at the beginning of firing.

[Wyndham]

There's a thing about glass/glaze. Glass wants to bead up to about a 1/4 in thick. So I believe that as the glaze starts to melt is pulls together and pops off and if there's moisture in the bisk from being too wet ,the steam pops the thick glaze, other wise the glaze just crawls down the side of the pot.

Just what I've seen in my disasters

Wyndham

[TJR]

Three things

1.Glaze was too wet when you loaded the kiln. Let pots dry for a day if thats possible.

2.Glaze is too thick. You did say two glazes.

3.It what biskpottery said. Colemaite/boron is a very violent flux. Your fritt contains this material.

Ain't ceramics fun?

TJR.

[atommat]

thanks to TJR

 

I recently had something very similar. I had a significant amount of colemanite in the glaze... I thinned it down and dried it off for a while longer and it seemed to do the job.

 

: D

[RuthB]

Questions, questions, questions! I've known Ghastly Borate to sputter, even in low amounts in a glaze, but not calcium frits.... Even with one that I've used a lot that is 90% Frit, frequently loaded right into the kiln. Have I just been lucky? I would be surprised, because if it can go wrong, it has. Perhaps mistakenly, I considered that sputtering was one of the main issues of Ghastly Borate and reason enough to avoid it. Somewhere on the hard drive, I have a post from the 90's by Karl Platt all about the bad behavior of GB. I will try to find it.

 

R

[neilestrick]

Questions, questions, questions! I've known Ghastly Borate to sputter, even in low amounts in a glaze, but not calcium frits.... Even with one that I've used a lot that is 90% Frit, frequently loaded right into the kiln. Have I just been lucky? I would be surprised, because if it can go wrong, it has. Perhaps mistakenly, I considered that sputtering was one of the main issues of Ghastly Borate and reason enough to avoid it. Somewhere on the hard drive, I have a post from the 90's by Karl Platt all about the bad behavior of GB. I will try to find it.

 

R

 

I've got to agree with RuthB here. Frits do not behave the same as Gerstley. Frits are pre-fired and have no LOI, so should not have the same issues as Gerstley.

 

We need to see the recipe for the blue glaze.

[RuthB]

Here's the post from Karl Platt on crawling and Gestley Borate

 

 

 

Date:         Mon, 4 Nov 1996 11:18:13 EST

Reply-To: kplatt@glass.com

Sender: Ceramic Arts Discussion List <CLAYART@LSV.UKY.EDU>

From: "Karl P. Platt" <kplatt@glass.com>

Organization: Glass.com

Subject:      My Crawling Glaze Has Ghastly Borate

To: Multiple recipients of list CLAYART <CLAYART@LSV.UKY.EDU>

 

----------------------------Original message----------------------------

This glaze, posted here yesterday, was noted to crawl:

 

 

Recipe: Percent Batch

Nepheline Syenite       47.30           2365

Gerstley borate         27.00           1350

flint (325m)            20.30           1015

EPK                     5.40            270

Totals:                 100.00 %        5000 gm

 

Also add:

cobalt oxide            1.00            50

red iron oxide          2.00            100

rutile                  4.00            200

cmc (mix dry powders well)0.15           8

 

The composition above bears little relation to :

 

61.61 % SiO2

14.23 % Al2O3

8.49 % B2O3

2.37 % K2O

6.55 % Na2O

6.72 % CaO

0.05 % MgO

 

I get something that looks like this:

 

        Wt%     Mol%

KNa2O   7.37%   7.85%

CaO     7.62%   8.99%

CoO     1.04%   0.92%

Al2O3   14.50%  9.40%

B2O3    14.19%  13.40%

Fe2O3   2.08%   0.86%

SiO2    53.20%  58.59%

 

I get numbers that look a lot different. For several of the raw

materials actual analysis were used and for others, the table in

Parmelee's book, which has never really failed me, are applied. Rutile,

as it is a highly fugitive material was not included in the calculation.

This is all to say that there are some descrepancies somewhere that need

to be reconciled.

 

The analysis furnished in the original post does not account for the

coloring materials. This is not a good thing to do as these can and do

profoundly affect the character of the glaze -- especially here where

we're looking at 1% CoO and 2% Fe.

 

Anyway, none of this has much to do with the cause of the crawling and

that is the use of Ghastly Borate. Ditch the Ghastly Borate and your

problems will vanish. Why? Well, once again, Ghastly Borate has lots of

water soluble borate. When the glaze is applied to the ceramic, the

borates are carried into the pores of the clay and ultimately form a

film between the body and unfired glaze. This film, being rich in

pure-ish borate, melts a lot lower than the glaze sitting on it. It thus

melts well before the glaze and prevents adhesion of the glaze once it

does melt -- it's a surface tension thing I don't want to go into now.

The effect can be likened to water on a waxed car. There are also

reasons why this effect is concentrated on rims, etc., which has to do

with how the article dries after it is glazed -- and perhaps with how it

was dried in the first place, but the core problem lies in the Ghastly

Borate.

 

The reason anyone bothered to invent frit was to solve problems like

this a long time ago. Why on earth does anyone still use Ghastly Borate?

Study a bit on frit and one will see that a foremost reason for

employing frit is to render borates insoluble.

 

>>if fired higher turns greener<<

 

This is related to the presence of TiO2

 

KPP -- Who'll use Ghastly Borate only if civilization ends

 

[Marcia Selsor]

I'd recommend putting kiln wash on the floor of your new Skutt just in case this happens again sometime and the glaze jumps the shelf.

 

Marcia

[Pres]

You might even want to invest in a faceted first shelf/kiln floor to get closer to the walls. I would also load questionable ware in the middle of the shelf to protect the walls. Glaze in an element groove can play havoc with the brick and the elements.

[Wyndham]

Anyone run into blisters/craters in float blue from the GB/rutile(cone 6). I'm trying to figure out if it's the standard 119 clay(bisk to 04) out gassing or the glaze. Inside the crater looks like a tan/cream colored material. The glaze is screened  at 80 mesh with no obvious foreign material on the dried glaze surface like sand or dirt.

 

FB gets greener as it  gets hotter on my clay body

 

Wyndham

[RuthB]

Anyone run into blisters/craters in float blue from the GB/rutile(cone 6). I'm trying to figure out if it's the standard 119 clay(bisk to 04) out gassing or the glaze. Inside the crater looks like a tan/cream colored material. The glaze is screened  at 80 mesh with no obvious foreign material on the dried glaze surface like sand or dirt.

 

FB gets greener as it  gets hotter on my clay body

 

Wyndham

Sounds like the soluble boron soaking into the bisque, melting very early, before the rest of the glaze ingredients have a chance and preventing adhesion of the glaze.

 

See the above repost from Karl Platt.....

 

 

Ruth

[neilestrick]

Anyone run into blisters/craters in float blue from the GB/rutile(cone 6). I'm trying to figure out if it's the standard 119 clay(bisk to 04) out gassing or the glaze. Inside the crater looks like a tan/cream colored material. The glaze is screened  at 80 mesh with no obvious foreign material on the dried glaze surface like sand or dirt.

 

FB gets greener as it  gets hotter on my clay body

 

Wyndham

 

Could also be from the rutile. FB is a notoriously touchy glaze. Also, I would stop using #119 for cone 6. It's not very tight, 3.5% absorption. Try #630, it's dreamy.

[Wyndham]

The center of the pit looks a bit like rutile tan. I normally use Laguna's  miller 55 but was out for a time, 119 is not my fav clay in any way.. Will 630 go to ^10?

I had an order for a FB cone 6 set of mugs.

No good deed goes unpunished heh,heh

Wyndham

[neilestrick]

No, 630 is a cone 6 clay. It's the cone 6 version of 182.

[Wyndham]

Thanks Neil