Rutile Glaze Came Out Grey

[AVPottery]

Hello,

 

Looking for some feedback about a rutile glaze I used the other day.  It was the rutile blue 1 in John Brits high fire glaze book.  I fired to cone 10, 9 at the top of my kiln.  All of the rutile came out grey, a few of the bowls that had rutile had some hints of blue starting to come out but mostly just grey.  They still looked nice almost like an ash glaze but obviously not what im going for.  

 

So my question is why?  Its possible that we over reduced? We had a cone 06 boat but it blew up when we fired the kiln right away.  The firing was about 8 hours using an 18" converted kiln running on LP gas.  Since the cone blew up we probably starting reducing about half way during the firing based on blindly guessing temp.  The kiln is an updraft because its an electric convert.  When the firing was done we covered the exhaust on top of the kiln to cool until the next morning.

 

Im planning on firing again this weekend and hoping for some different things to try and get the blue to come out.

 

Thanks for any feedback,

 

-Andrew  

[High Bridge Pottery]

Needs to be thicker, which rutile blue was it in the book?

[AVPottery]

It was the "rutile blue 1".  I would be skeptical about thickness.  I had a vase that that I had done all in rutile blue.  It was pierced so it was a disaster to glaze and ended up with all of these ridiculous thick spots.  Easily 1/8" to 3/16" inch thick in my spots.  Ill have to post a picture but those thicker spots turned out lighter than the thinner spots.  Overall the glaze was relatively thick in application and had lots of glaze runs which added thick areas.

[Mark C.]

 This thread viewed best with Mission Impossible Theme song in background turned up LOUD

 

All rutile glazes base glazes are very fickle-meaning they are hard to work with.

I use a lot of rutile base glazes and firing reduction and temps are key to how they look.

The kiln you are using fires so unevenly a constant result will be  close to impossible

but should you accept the mission Andrew I suggest experimenting with glazed tiles spread around on the different layers next to some cones.

This message with blow cones up in 20 minutes

should you recreate the effects you want or be captured the- potters council will disavow all knowledge of said attempts

 

PS if you or your fellow team members try this again try having the same tile have at least two thicknesses of glaze on them.

Rutile base also loves to pit.

[glazenerd]

Mark:

Rutile light is suppose to be 2% iron or so, and Rutile dark is suppose to be 10% iron. This play any role?

Nerd

[Mark C.]

Its the mystery of reduction-my base has no iron

I think of rutile base as just rutile-iron  additions will muddy the waters

[AVPottery]

Mark,  Thanks for the laugh, I do choose to accept this mission.

 

My current recipe is just the standard base (Custer, Feldspar, Whiting, Kaolin) with just 7% Rutile.  This is John Britts "Rutile Blue 1"

 

I am also going to try changing the Reduction cycle, Im pretty sure we must have started reducing pretty hard way to early.  John B. has some reduction charts that show starting reduction near Cone 012.  I now have a temp probe so I will give this a shot tomorrow.  I will follow the R3 reduction cycle he shares.

[Mark C.]

My rutile base glaze likes cone 10 to cone 11 in a nice reduction spot to work well-its orange color if fired cold or clearish if unreduced.

I do not have any experience with Johns glaze.

[AVPottery]

My rutile base glaze likes cone 10 to cone 11 in a nice reduction spot to work well-its orange color if fired cold or clearish if unreduced.

I do not have any experience with Johns glaze.

 

Mark would you be willing to share your rutile glaze so i could see whats different?  maybe even try a second rutile while I am firing 

[High Bridge Pottery]

I thought with it starting to come through in the bottom of bowls that it needed to be thicker although now I read your post again there is no mention of bottoms.

 

I had a rutile blue, oxidation and with cobalt in that would be a brown where thin even with cobalt colouring it blue.

 

What kind of burner do you have? 

[AVPottery]

I thought with it starting to come through in the bottom of bowls that it needed to be thicker although now I read your post again there is no mention of bottoms.

 

I had a rutile blue, oxidation and with cobalt in that would be a brown where thin even with cobalt colouring it blue.

 

What kind of burner do you have? 

 

The burner is a Summit GV-18.  Fires LP with about 100k BTU, two burner orifices firing through the bottom two holes.  The Kiln is an old burned out electric 18 inch kiln.  Probably about 26-28 inches deep. 

[Mark C.]

 

My rutile base glaze likes cone 10 to cone 11 in a nice reduction spot to work well-its orange color if fired cold or clearish if unreduced.

I do not have any experience with Johns glaze.

 

Mark would you be willing to share your rutile glaze so i could see whats different?  maybe even try a second rutile while I am firing 

 

check your pms

[High Bridge Pottery]

Can you crack any of the pots open to see if there is carbon coring? Could be difficult not to fire in reduction from the start.

[AVPottery]

Can you crack any of the pots open to see if there is carbon coring? Could be difficult not to fire in reduction from the start.

 

Here is a picture, not sure what it means....

[Callie Beller Diesel]

No carbon coring there.

I can see that the glaze is too thin, though.

[terrim8]

I agree about the glaze being thin. I used to do two good dips with rutile blues. I also used to put a few iron stain brush strokes on the pot first - it seemed to bring out more colour in the rutile glaze. 

[Mark C.]

OK a photo is worth a thousand words

Your glaze is to thin as noted already

It never occurred top me you where using stoneware clay-so this makes your quest even harder

When I threw mostly stoneware my rutile would often pit and look like yours

When you apply this same glaze to porcelain you will find instant better results .

stoneware with its iron content will make your quest very hard-my best suggestion is get Tom Cruise on your team

[Babs]

Or a porcelain slip on your stoneware.....may be more reliable that the above person..

[High Bridge Pottery]

It's interesting how grey it is inside compared to the toasty brown outside, not what I was expecting to see though. Any gas kiln I have fired without air controls have carbon cored the pots. After reading up about this a bit more I am now even more confused about what reduction is and the coring seems to be more a clay body thing.

 

Is the toasty brown from re-oxidising the outside? Is it better to have the whole pot with an even reduction and not this outer oxidised skin or am I thinking about it wrong. Doing a bit of a search I found an old thread talking about reduction and coring. http://www.potters.org/subject83977.htm

 

It's interesting what you find when you start to look deeper. I always thought it was to do with the iron going to FeO but this paper seems to say otherwise. Talks about it being reduced to Fe₃O₄  and some reactions between Ca and S https://www.researchgate.net/publication/229296099_Calcium_and_sulphur_distribution_in_fired_clay_brick_in_the_presence_of_a_black_reduction_core_using_micro_X-ray_fluorescence_mapping

[Callie Beller Diesel]

rutile blues, or "floating blues" need to be deep enough for something to "float" in. They're a non-homogenous melt, which is why they're so persnickety. I don't think the brown colour is re-oxidation. The OP mentions they're firing in a small electric conversion, which means you don't have the thermal mass to cool slowly and allow the pretty crystals to form.