The Child is Father to the Man

Gilad, my son, writes me an email from his culinary studies in California to remind me (a propos that gas firing) that things aren't meant to go right first time so that you can learn something from your mistakes, & how right he is. Teach your parents well,as CSN&Y sang all those years ago.

So-So

The results from the first gas firing of the crystal glazes were less than sensational - some glazes too thin,some traces of reduction,but mainly crystals that grew too large,which you would think would be good,but they merged into one another and rather obscured the background [the silver vase] - an interesting effect,but not what I'm looking for.But the sink didn't crack,which is hopeful,one tall green vase came out well [on the right],and I've fired another electric kiln which came out very nicely,and I've made a couple of adjustments to the gas kiln setup,and started glazing for round 2, probably next week.

Back in Fashion - the Drain-Pipe

As mentioned below; a great way to glaze tall thin pieces with not too much glaze.The bottom is pushed into a pad of soft clay slightly larger than the pipe's diameter. I found this discarded offcut recently - it really needs a bit of a trim [or bris as we call it around here] - even I don't throw this tall and thin,and it's difficult to see what's going on down there when you're glazing.

The Big One

The time has come;
I'm firing the first batch of crystal pots in my gas kiln. I reached top temp half an hour ago,trying hard not to let the kiln reduce [difficult when trying simultaneously to maintain a decent rate of rise of temperature],turned the kiln off,and have just relit it at 1080 degrees for the first 45 min. soak of six,each at a lower temperature. This is how I used to fire the crystals [for 20 years or so] until my old gas kiln couldn't take the strain,which just coincided with the time I learned to throw big[ger] pieces in porcelain. My small electric kiln has been a wonderful learning tool,and has produced some little gems,but it's small. I'm hoping that my new-ish gas kiln will give good results and justify the effort of manual firing - there are 4-6 hours now of sitting with one hand on the gas pressure tap making occasional minute adjustments to keep the temperature stable.
Only the top half of the kiln has pots in - the bottom is invariably too cold in an oxidised firing - and one of those is one of the sinks,which,as you are aware,are prone to cracking: I may have taken too long to reach temperature,or allowed a whiff of reduction to sneak in,either of which will wipe out the crystals: some of the tall pots were glazed with the charmingly-named fou-fou[a breath-powered spray] with which I have little experience,others in a tall length of plastic drain-pipe,both methods making the critical glaze-thickness hard to judge - in other words,I may well be wasting my time for the next few hours,not to mention the gas it's consuming. On the other hand,if my guesses and gambles pay turn out to be near the mark,we may see some fireworks tomorrow...

Fourth Firing

Crystal glazes are notoriously difficult to photograph,and I spent quite a while messing with camera settings to get these shots without too much subsequent digital fixing - but I hope you can appreciate that the firing came out nicely! By now I've done so much [needed] testing with these super-fiddly glazes that I haven't really got enough left in each bucket to glaze the larger pieces that I hope to fire in the gas kiln [which will be a whole other story from the small electric kiln with its automatic controller]. Undaunted [and maybe I should be daunted] I'm going to try some inventive techniques for getting the glaze on,at least for one firing. A sink is already glazed and sitting in the kiln...Shabbat Shalom!

2nd Electric Firing

I used the old batches of glaze,wanting to see some semi-predictable results; I changed the program slightly,increasing the soak time at each stage of the crystal growth [I think there are 6 stages on this particular program] by 3 minutes - and the resulting crystals are indeed slightly larger than the previous firing. But since the pots are the same size,bigger crystals mean less background and more crowding,so on the current firing [approaching 1000 degrees C as I write,with another 4-5 hours of firing to go] I raised the temperature of each stage [to thin out the number of crystals,maybe] and reduced the soak just a bit. I'm also testing new batches of glaze after getting a delivery of raw materials.
If this all seems too technical,please have patience. I'm writing these details down to remind myself - if they're of any use to a fellow potter,all the better: if you're not in the business,maybe you'll get an insight into some of the finer nuances of the craft [and understand why you pay more for these crystal-glazed pots when they do work.]

Cracks

Another one bites the dust - also the bottom one of 3 in the bisc kiln [how else can I fire 3 big sinks in one go?],also cracked [among other paths] through the stamp on the side. I even tried firing this bisc a bit slower. So now I know that either the position in the kiln or that stamp is causing the trouble. Probably. Or at least ~I think I know. Now I just have to remember it 'til next time...

Plink

The title above is a link to a short video - filmed,edited and posted from my iphone - of the approved technique for removing pedestals from crystal glaze pots after firing. If you sand bisced pot-bottom and stand and attach with kaolin/glue mixture,the parts should separate with that satisfying and informative Plink. If you keep on heating,the pot will break shortly thereafter. How do I know? Guess..
Top picture: improvised camera support.
Middle: Testing remains of last year's glazes - they still work. Some opinions hold that these glazes have a limited shelf-life;I've never found that to be the case.
Bottom; left - blue crystal glaze with no titanium;there are no 'seeds' for the zinc to form around,so just masses of micro-crystals. Right - same glaze with 25% of it's titanium; looks like too much cobalt [too blue],but some blue crystals with clear blue background. This is what I was hoping for - a couple of years ago I had a beautiful blue crystal glaze,but subsequent batches gave me only blue with a tan background - nice,but not as. Numerous experiments got nowhere,then last Summer it suddenly popped into my head that I had run out of titanium when mixing that particular blue/blue batch and forgotten to write down the difference. Now I think we're back on track - a bit more titanium,a bit less cobalt,maybe a smidgen of manganese for the colour...
By the way,my joy at getting 3/3 sinks from the bisc last week was premature;my friend Alan pointed out a crack to me that evening,running smack through my signature stamp on the outside wall,trim to base. I've had this happen before,and even took care to stamp the sinks especially gently,but it wasn't enough.Next time I'll carve my signature - or maybe not sign at all. There can't be that many other people making crystal-glazed porcelain sinks. The one that cracked [I gave it to a neighbour for a planter] was on the bottom of the bisc kiln,although raised up a little - another contributory factor,I think.

This Evening's Sunset

 

Turquoise

While firing the bisc in the gas kiln yesterday,I also fired a quick oxidised firing in the small electric kiln [to give the elements a protective coating,you remember] and got these barium matt vases.

Much to my Surprise

All three sinks survived their first brush with fire. I'm loading the bisc kiln again with the remaining 3 sinks and the rest of the pieces for the crystal glazes - there's some room left for a bit more throwing to fill it up...

That's Better

I finished loading the bisc,so now all that scary balancing business is out of sight. When I close the kiln door it looks even better.

Precarious Bisc

What do you think? There are 3 more sinks for a second bisc,and not many ways to load them with tall vases for company.I'll be moving round the studio with extra caution 'til this lot is fired...

Crystal Time is Here Again

I've been working for a couple of weeks now throwing porcelain pieces [and enjoying myself greatly],preparing mentally for the ups and downs of another round of crystal firing. I took out the old elements from the little electric kiln [the one in the picture] and replaced them with a shining new set; today,after a couple of bisc firings with the new elements,I mixed up a batch of my only 1250 degree/oxidised glaze from way back - a turquoise Barium matte that I only use for the occasional test-kiln-ful of hamsas,and glazed these 5 bottles for a cone 8 firing. I'm doing all this to try to get a protective oxidised coating on the new elements so that they won't fade so quickly when the crystal firing starts to form crystals inside the metal of the elements. Obscure practice,no?
I'm also hoping that my new gas kiln will fire fast enough [while staying in oxidation] to take some of the bigger crystal pieces [sinks and tall vases]. There's no controller on the gas kiln,so the whole firing has to be done manually - but that's how I did it for 20 years or so,until the gas kiln got too old,slow and clogged for the crystal firings.