Saturday, November 13, 2010

Crystalline Glaze Firing Unpacked

Close up of crystalline glazed pot with titanium, iron, and cobalt

This morning I unpacked another small load of crystalline glazed pots from my electric kiln, and filled the kiln up again with pots for a bisque firing which is taking place as I write. (By-the-way, I notice that Blogspot has put Friday at the top of this post... well, it may be where ever Blogspot lives, but it is Saturday here!)

Two crystalline glazed pots, the one on the left has titanium, cobalt and manganese in the glaze.

I had started off the glaze firing on Wednesday evening and got up at intervals through the night to check progress. By 5.15am the kiln was at 800 degrees Centigrade and reached 1260 degrees Centigrade at about 9am, and with cone 9 down I switched off. An hour later the kiln was at 1090 C and I switched on again and began the part of the firing where the crystals were allowed to grow. I held the 1090 temperature as closely as I could (I have a manual kiln). Three times in this growing period I switched the kiln off, and let the temperature fall to about 1030 C, then I held that for 5 minutes, then brought the temperature back to 1090 C again. Every time I did this, I caused a growth ring to form in the crystals. I switched the kiln off for the final time at 4.30pm.

Close up of the pot on the left showing well formed growth rings in the crystals.

Through most of the 6 and a half hour crystal growing period, I checked the kiln about 50 times (I can tell that from my kiln log), which meant a trip out to the kiln shed each time. Good exercise, and much needed! At the same time as doing the firing, I was sorting out paintings and pots to go to a local art and craft exhibition (Laura and I are guest artists), writing and printing an illustrated price list, packing the paintings and pots, and delivering the work to the exhibition at our local village hall.

There were some interesting pots in this firing, particularly where
I had put two different crystalline glazes over each other,
something I intend to do more of.


In addition to all that I opened our gallery, and tried to do some house work . Laura had been away in the North Island staying with her parents who celebrated their 50th wedding anniversary, so I wanted the place to be a little bit orderly for when she returned!.

A small addition of manganese seems to make 6 sided shapes appear in addition to the round crystals. It is an odd effect as the shapes reflect the light like lenses, but are almost invisible when looked at straight on.

I didn't succeed in making as much progress with the house as I would have liked, but my endeavors did uncover something horrid under the little rug in the kitchen...

I find it useful to put nearly dry work on top of the kiln whilst it is firing. If you look carefully you will see that I like to sit the pots on a wire rack or on kiln furniture to allow the air to circulate around the pot, and to prevent the pots from getting too hot.

... 4 dead and flattened lizards! Yerk! Nigella had been catching them (I have found her with others), but I had not realized that she had also been posting them under the rug!

One of my glaze testers showing very strong, dark growth rings
The glaze contains some titanium, manganese and iron.
The
glaze testers are that funny shape in order to catch the run off glaze.


In the evening I drove out to Dunedin airport to meet Laura, and had her home just after 9 in the evening. It was quite a long day really.

This is a similar glaze on a vase, in this case the markings are quieter than on the glaze tester. The thermal mass of the pot, and its position in the kiln have quite an effect on the way that a glaze turns out. A small pot may react faster to changes in temperature in the kiln.

Laura had a good time with her parents, and quite a number of family and friends were able to get together for a celebration with them. Laura's parents were married on 5th of November (Guy Fawkes Day), so Laura was delighted to be able to purchase a few fireworks to let off in the evening.

This was the largest pot in the firing at about 10 inches high (255mm)

The largest pot that I fired has some really subtle effects in the "background" that surrounds the crystals. The colour graduates from the palest blue at the top, through yellows to green in the lower part.

Here is the entire kiln load... not many pots really, but for these glazes it is probably best to keep the pack in the kiln fairly open to allow it to heat up and cool down quickly.

Tomorrow I have to smooth the bottoms of the pots. I had time to separate them from their glaze catching saucers this afternoon, and to do a basic smoothing of the worst of the glaze runs with an electric bench grinder. Tomorrow I will finish up by hand.

I did promise you more photos of my journey down the length of New Zealand..... but it is now nearly 10.30 at night and I need some sleep.. So I will try again next time!

21 comments:

Linda Starr said...

Oh I like these new crystals with the obvious growth rings, so interesting to hear all about it.

When you separate the pots from the catch basins, how do you keep the glaze from cracking part of the pot off along with it.

fifty years that's a very long time. I am sure Laura had a wonderful visit.

Have a great sale at the show. Curious about the illustrated list, could you talk more about that?

cookingwithgas said...

oh- they got better and better as I went down through the post- I felt like Alice down the rabbit hole with something new at every turn.

Oh- lovely presents form the kitty!
Best to you both- and the kitties!

Brian said...

Love the growth rings and the manganese hexagons. Quite an accomplishment with a manual kiln!

You might want to double check you time zone setting in Blogger, under Setting > Formatting tab.

ang said...

wow peter you've outdone yourself!! ab fab crystals happy grinding tomorrow :))

Hollis Engley said...

Lovely stuff, Peter.

Pat - Arkansas said...

Although I don't understand the complexities of your work, I very much enjoy reading about the processes you use in making your wonderful pots/glazes. The end results are both marvelous and beautiful. If ever you decide to discard your glaze testers, I'd be happy to send you my address! Lovely, lovely!

Peter said...

Hi Linda,
Some good questions there that are actually worthy of a reply in a post (which I just might do). In brief though, the pots sit on little stands that I make from insulating fire brick. These are between half an inch to an inch thick and are shaped to match diameter of the pot that they are to sit under. These stands are positioned in the middle of a glaze catching saucer and prevent the pot from submerging in a puddle of glaze. Glaze is like a corrosive substance at high temperature and will chew its way through insulating fire brick, so this needs to be carefully protected. I make up a creamy solution of alumina and water with just a little china clay or ball clay and coat the saucer and the stand with that. The alumina also acts as a non stick coating and allows the pot, and its glassy runs, to be removed fairly easily. I carefully work around the glassy join between the bottom of the pot and the insulating fire brick stand with a chisel that I tap lightly with a hammer. If I aim just below the bottom of the pot, the glaze runs that I cut through are only supported behind by the soft insulating fire brick, and I can cut through the glaze runs quite easily and the pot separates from the stand. After that is the grinding smooth of all the jagged sharp bits.
Like everything else, there are other alternative ways of doing all of the above, some of which I am trying, but the one I use does work fairly reliably.

Regarding price lists. I have started to use little thumbnail photographs of our artwork with the usual information beside them of title, medium, and price when I do a price list. I think this makes it very easy for people (and gallery owners) to know what they are looking at when they walk around the exhibition. With my pots, in particular, I find it almost impossible to come up with titles, and written descriptions can be ambiguous. The price list is one place where "a picture is worth 1000 words"!!

Peter said...

Hi Meredith,
That's nice! I wish the cat would bring us something more useful or appetising. Ginger did look quite interested in sheep at one stage, and used to stalk them in the paddock next door to our place, but he never brought one home!! Which was just as well:), but Nigella and squashed lizards.... yuck.

Hi Brian,
Good to hear from you, and welcome to this site. I have followed your advice and have managed to reset the time zone on this blog. Thanks so much for that. I had missed that somewhere when I was setting up the blog in the first place, and the time was to Pacific Zone (which I guess is slightly confusing for us here... in the Pacific), but we are really Auckland as far as time is concerned. So now the post says "Saturday" Yay! Thanks too for the word "hexagons", I was so tired last night when I wrote the post, that I just could not recall the right word for something with six sides!
I am interested to know if you are a fellow Linux user? I see you have a "how to" article about the "Gimp" on your site. I know that this useful application has also been ported for Windows, so that may not be the case, but???? (I do also use the Gimp for some of my photo editing).

Hi Ang,
Mmmmmmm.... it's back to the grindstone!!

Hi Hollis,
Lovely to hear from you. Thanks for that.

Hi Pat,
As a matter of fact I would love to, and something along those lines has been in my mind for a long time... Please do email me with an address... opogallery AT gmail DOT com

Judy Shreve said...

Oh Peter these pots are incredible! You are getting some fantastic crystals. I love the way you add a 'dash' of manganese to the glaze - And it is amazing that you do your firings and achieve these results in a manual kiln. Good work!

Arkansas Patti said...

Your pots are spectatular Peter. You really are a master.
As for the lizards--do you think they might have caused the bad gas? Mighty dog eats sun dried earth worms(only when I am not watching) and it gives him lethal breath.

Cindy Shake said...

First Peter I was struck by that incredible titanium, iron and cobalt glaze, then they just kept getting more fantastic! THEN I saw the forms before you added glaze and was IN LOVE with all of them -you do wonderful work :o) always such a visual treat and delight to read!

Peter said...

Hi Judy,
Thanks for that. I do end up reverting to instinct rather than science when I am actually splashing around in the glaze bucket! Probably I am a bit lazy too, but sometimes a "dash" does give nice surprises! I do try hard to get the firings right though. A manual kiln is work, but there was some fantastic work done with crystals before the era of electric kilns, and I do wonder how big coal fired kilns were made to fire crystals! It is a mind boggling thought.

Hi Patti,
"Master".... noooo! but I am enjoying what I am doing and trying to learn all the time. The gas from lizards theory is a seductive one..., but I think the gas from not tolerating a certain brand of kitten food is more probable... and repeatable!!

Mighty dog's lethal breath from sun dried earth worms reminds me of a documentary I once listened to, where someone was putting forward a case for farming earthworms as a useful form of protein. Evidently they would feed the world far more effectively than some of the other life forms that are grown on farms... I guess the idea was to mash them up and turn them into something like those meat substitute cubes that some meat craving vegetarians add to their meatless stews and pies! If Mighty dog is anything to go by, it is just as well that earthworm protein hasn't become a commercial reality!

Hi Cindy,
Thank you so much for your encouragement, it means a lot coming all the way from Alaska! Titanium Dioxide is a fascinating substance in glazes and also does nice things in the reduction atmospheres that would be found in a wood fired kiln. I think, and someone might correct me if I am wrong, that titanium is causing the nice flecking and good colour response from the iron in the iron and cobalt glaze (detail first photo on this post).

Brian said...

Peter,
Yes, I use Linux/open source software whenever and wherever I can. Gimp is a favorite, and Open Office.
Glad I could help get you into the right time zone!
Keep up the great work with the crystals.

Peter said...

Hi Brian,
Good news! Horray for open source and Linux! I've been using Linux operating systems for 7 or 8 years now and am enormously thankful to all the people that put the hours into developing such things. Currently PCLinuxOS for the desktop and Ubuntu netbook for the netbook, but several others have been used and enjoyed in the past.

Armelle said...

Hi Peter,
What a great work with such manual technique !!! Can't wait to see the next load of the beautifull pots at the top of the kiln.
I took a glimpse to your website too, so interesting and well explain.
Laura had a great time, so nice !!!

Best wishes to you, Laura and the Hunter and the Ginger.

Hannah said...

Mmm, flattened lizards - lovely. Mind you I almost think I'd rather have them than the huge fat juicy slug that was sitting across the inside of the kitchen door handle yesterday. Yuck.
I am still stunned you are doing all this with no electric controller, it's a fantastic achievement.
best wishes,
h

Peter said...

Hi Armelle,
Lovely to hear from you. Regarding the website, Thank you for having had a look. The site is still under construction and I will be adding to it, but I hope to have a gallery of my work and also some articles about potting there so they are easier to find than on my blog.

The Hunter of Lizards sends 6am purrs! :) The rest of the family are probably sleeping!


For those who haven't seen it yet, there is a link to my site at the top right of my blog... My Pottery Gallery... https://sites.google.com/site/petergregorypottery/

Hi Hannah,
Not sure if flattened lizards would ever make to to top of my grocery shopping list, and huge, fat, juicy slugs are a formidable sight when encountered rising from a pile of lettuce in the middle of a nice salad... and definitely a nasty surprise on any door handle... Sometimes I have wondered if slugs and snails would taste anything like shellfish... but have been too squeamish to try!

Avi said...

Hi Peter,

First off nice pots and beautiful crystals!! You are doing some great work considering you use a manual kiln. Here is a suggestion if you can find one at a reasonable price in NZ or shipping is not too much. If your kiln is within 60 feet of a TV in the house this might cut down on the Kiln Trips.

http://picasaweb.google.com/AviHarriman/SecurityCamera?feat=directlink

It is a closed circuit TV camera. I use one to monitor my kiln eve though I have an automated controller.

Also do not forget the Nickle, just leave out the Titanium. An example:

http://picasaweb.google.com/lh/photo/H3GIShL8csqnRcGqGFWL2g?feat=directlink

Keep it up,

Avi

Aude Terrienne said...

Hello,
I know your blog from Armelle's one.
I like your glazing, specialy the brown one.
Have a good day.
Aude

Angie said...

Wow ...stunning pots ...love the brown tester with all the dark rings.... this glaze medium is your forte .xx

Peter said...

Hi Avi,
Thanks for the tips. I like the security camera idea. It certainly could make things easier at times. (Occasionally I have thoughts about some old radio control equipment that I had for model aeroplanes... it would be possible to rig up servos to work the simmerstat controls on the kiln. A camera to show me what was going on would really complete the Camera Monitored Arm Chair Kiln Operation Package... CMACKOP for short!). Thanks for the photo of the vase too, it looks lovely, and it is interesting to see nickel in action. I really must continue testing glaze bases with nickel.. it would really extend the possibilities.

Bonjour Aude,
Thank you for writing. It is really good to hear from you. Sometimes I visit your blog when I go to Armelle's:). I am glazing more pots today, and hope to fire them before the end of the week. The brown one is interesting, and I will certainly try it again.


Hello Angie,
Good to hear from you. The dark rings are the best ones yet. I fired more accurately than usual. So sorry to read on your blog that your cat Buffy died. You will miss her greatly. I'm sure that all of us who love cats send you our kind thoughts and sympathy. xx