Building 'Theophilus' Kiln', Part 1 - The Structure

I'm having quite a lot of fun this evening playing with clay. It's difficult to call it anything but play -- I have minimal clay training or experience. I think it will enrich my master's degree thesis, however, if I construct a medieval-style kiln to understand that experience and process. 

I've only found historical information on two kilns -- One is the kind documented in Theophilus and which has a recreated example in the Centre International du Vitrail just next to Chartres Cathedral, in France. The other is a late Gothic/early Renaissance brick kiln from Amsterdam, documented in a manuscript in Antwerp which was transcribed in 1974 and analyzed by Joost Caen in his doctoral thesis and related publications. Of the two styles, the earlier is more appropriate for my formal research but I'm fairly sure I'll have to try the later model for SCA purposes before too long.

"Chapter 22. The Kiln in Which Glass is Fired

Take some flexible canes and fix them in the ground in a corner of the building with both ends aligned to form a series of arches, a foot and a half high, the same in width, and a little more than two feet long. "

The skeleton of this project involved a number of necessary modifications. I was building this kiln in my garage, and while 10-cane could probably handle the impact, I am just not strong enough to get them into the concrete floor. Further I'd love to be able to take this to SCA events or similar educational activities, though at this point I probably can't lift it alone. From the start some kind of platform was planned. I used hardwood/birch plywood as the base and attached four corner brackets on the bottom. At the time I thought I could use the brackets' holes to string rope for lifting, and now I laugh at the folly of youth. They do serve their secondary role of table legs quite well, with no apparent strain yet. 

The top surface of the board I covered with thinset (cement) and then covered it with stone tile. I'd like to avoid doing all this work again for a couple of years at least, and I hope the stone level between the kiln and wood will add some longevity to it.

I have some limited experience working with clay through the Chicago Mosaic School's fantastic classes [Go check them out, no I am not paid to say this], so initially I threw a bit of clay down, tried to practice wedging, building clay, really playing with it to get the sense of how strong it is in different ways. This wasn't related to the project in any way, but I mention it because it inadvertently gave me observations later along that I would have missed. 

And for 30 blissful minutes I was a 12-year old with Legos and Play-doh

I asked friends for suggestions where to buy basketweaving canes, and this lead to the generous Donna Weeks coming way out of her way to give me a few hours of basketweaving education AND spare materials. I knew nothing when I placed my own order before this demonstration, and figured size '10' canes (the largest) would be the most appropriate choice. Every basketweaver who asked, I told this to, and universally everyone was shocked. I understand this now, I'm pretty sure size 10 cane is produced by folks from the rebar plant in their free time. Much good came from this lesson, however, and several hours of wasted time avoided.

I had intended to stick the ends of the canes into clay, and allow the clay to hold it in place. "Allow" as though I have any real say in the matter, when in fact the 10-canes were giving the orders. The clay was not going to hold the canes in form (yes, soaked). I continued with the idea of making a "basket upside-down" and made a wooden shape to hold the ends of the canes, which stood in perfectly for packed-dirt in my glazier's shed outside Sées... oop, sorry, I'm back. Here came an important lesson: When I said I made a wooden shape, that's probably barely legally defensible. I used a chunk of MDF I had in the corner of the garage, without thinking about it at all. Cut an oblong horseshoe-shape out, drill holes just big enough for 10-cane. Those canes, which had been soaking in water. Onto a bed of clay, fresh out of a sealed bag. That's a lot of moisture hitting thin MDF from all sides.

So it began disintegrating very quickly and I had to start tying reeds together to try and maintain the shape.

Oh, also, I took the opportunity to practice basketweaving. Don't hold the results against my teacher!

So yes, use real wood.

"Then vigorously knead some clay with water and horse-dung in the proportion of three parts of clay to a fourth of dung. After kneading this very well, mix with it some dry hay and make long loaves out of it. "

I'm sure I'm not alone in that every once in a while I stop to examine my life and try to figure out what specific mis-step lead to voluntarily spending a nice fall Saturday trying to track down horse excrement for my latest mad engineer experiment. After contacting local horse ranches/therapy facilities, most of whom were more than willing to let me cart of their refuse, my friend Kate came through with an offer to assist a few days sooner than the horse facilities could, which meant a whole weekend more I could get done. I took a plastic tote (15 gallon size, I think) lined with an industrial garbage bag, got to meet the horses, and drive off into the distance with a considerable amount of road apples. Trunk apples?

Three parts of clay to a fourth of dung. The interesting thing is when measurements are given in "parts" it's usually because volume and weight measurements are interchangeable (think baking, where many ingredients are so similar). I could not say the same about pottery clay and horse leavings. I have a possible side-project of testing both volume and weight compositions, if I can figure out the best way to do such a test.

I'm going to talk a bit about making and working with this clay mixture. However, since I know the subject can cause a visceral reaction to some people with sensitive stomachs, everything from this paragraph to the next picture should be black-on-black text. You can read it, if you want, just by highlighting it.

Edit: Ok, that didn't work. FROM HERE:

The before-mentioned Donna came up with the great term cloop, a portmanteau of clay and poop that is much less evocative to the imagination. Some people seem to consider this a form of cob (as in cob ovens, cob buildings) but I'm not finding highly consistent usage. Cloop, it is.

If this whole idea is leaving you with doubts, let me assure you it is not remotely as bad as you would expect. The faint smell in the close vicinity of the tub disappeared in a day. The first several days I worked on it, I wore latex gloves which inevitably tore up within ten minutes. Eventually I gave up and took relief that I had filled a bucket with water beforehand I could use to scrub a millimeter off my hands before going back inside. Nothing about it is reminiscent of dog, cat, human, etc. waste, and really it feels and looks like something you'd buy at the garden center, like a fine mulch. 

I went with the idea to go by volume. It seems widely-accepted that the organic additions of dung and clay are to build pockets of air to change the clay's thermal properties. Volume seemed more natural for that choice. I did not use any modern measuring tool and just did it by visual approximation.

For the longest time I would tear out a fist's worth of clay, flatten it into a flat disc (it took me seven tries to find a phrasing that was in no way connected to food). I then added the equine component... and started mashing it. I think that the most effective technique I found, at least initially, involved rolling the cloop into tubes, folding them in half, and repeating the process in order to get many layers. Then just a bit of random squishing. I didn't decide this until later, but the easiest way to add a reasonable amount of hay was to put hay down on a workbench and just dredge the cloop like breading (Oops, sorry). Kneading it in with no particular technique yields a sturdy ball or log of material quickly. I noticed that after an hour of making these I stopped really measuring it all out. The cloop has a certain visual quality to it, and the hay adds so much rigidity, you can quickly just get a feel for your normal. 

I did try, one time, to mix it en masse in a bucket. PLEASE, do not try it. The only problem with hand mixing it as above is that your hands will get tired quickly. I did find that taking larger (say double) portions and kneading it on a covered workbench like dough (sorry). It felt like it went quicker without straining my weak nerdy limbs. 

Thanks to my initial goofing off with the clay, I realized how different the two are in properties. When I made a slab of plain clay, it dried while I worked with it and was not easily indented hours later. When I made the base slab of cloop, it was easily indented 36 hours later (both were uncovered).

To HERE.

Cloop!

While I was working on the base, I was plagued by a beast which is famous for having plagued monk-scribes.

"Cover the arch of canes inside and out to the thickness of a fist and leave a round hole in the center of the top, big enough to put your hand through. Also make three iron bars a finger thick and long enough to reach through the width of the kiln. Make three holes for these on each side of the kiln so that you can put them in and take them out whenever you wish."

At this point, it's a building montage.

This is the view peering down into the chimney which can be seen in other pictures in the back of the roof

The walls are between 2" and 3" in thickness everywhere I measured. The cob oven bakers in my life said they aim for 2½" to 3½", and beadmaking furnace friends said at least 2", so I feel like this is a solid range. 

I'm trying to let this boulder dry naturally for a few days, occasionally hit with a heat gun, before I follow Theophilus' last step:

"Then put fire and wood into the kiln until it is dried out."

For Part 2, I plan to write-up firing the kiln (including its door) and tests on how long it takes to heat up, likely using various fuels, etc. I'd like to have a fairly predictable firing idea even without modern measurements, and I don't have 4-6 free years to fake an apprenticeship and learn the timing by trial and error. I have 4 high temperature thermoprobe sensors I can use to take some measurements. 

For Part 3, I plan to document firing a piece of glass in it, or several sample chits using period formulas which I'm incorporating into my MA thesis.

Glass and Gold and Gilding

I've signed up for a couple of mosaic classes in April and May. It reminded me I wanted to try my hand at making Byzantine-style tesserae, and then a friend's Facebook post kicked me into high gear. She had much better success than I did and shared some of her wisdom. My test piece:

Two pieces of clear fusible (Bullseye CoE 90 Tekta clear) with one layer of gold foil sandwiched

Rhode Kephalaina let me know in her sample chips, marked 1 and 2, thats the sheets of foil. So, chip '1' has four layers approximately, and '2' with 8. My samples above are 4" square, not 1", and had one layer. It's not exactly ugly! It's just not the beautiful gold glass expected. The nicer parts of mine are where the foil doubled on itself (see Lessons learned, below...) I know now to fix it, though, thanks to a conversation with Rhode.

Ive also fallen for verre églomisé. Predating Rome, pretty much, this art (gilding glass and painting the back black) was practiced through the Roman period into modernity. It gets its name from an art collector 200 years named Glomy. It turns out it's not super difficult!

Sorry it's sideways. I can't quite remember how the technique entered my awareness, either through researching mosaics or mirroring. A little gelatin, some gold leaf, and some glass. A fine needle to scratch it up, and black paint. I'm going to teach a class on it at Pennsic this summer, which is exciting to me. I've tried a few types of leaf, a few tools to transfer it to the size, and will be picking up a second (larger) gilder's tip this week. It's beautiful to look at and I'm excited to see how I can integrate it into stained glass and mosaic work.

Probably To Be Continued...

Lessons Learned:

• Transfer foil is a lot better to work with for verre églomisé.
• Tiny creases are almost unavoidable with loose leaf, but the gelatin size flattens them out as it dries. The end result isn't perfect but it is much better than what you start with.
• TURN OFF YOUR CEILING FAN. Many people remark that gilding can be done at your kitchen table, and they are quite right. But when you bought a book of loose gold leaf and have the fan on medium, you are going to make a kaleidoscope of tears and gold for a moment. 
• Making Roman Gold, as Rhode is trying, or Byzantine Tesserae as I am, costs a bit! The leaf is not terribly cheap, though you can find it reasonably. She speculates gold foil, not leaf, would work better but it runs $75/5 sheets. 
• Don't use imitation gold. I did this before a year or two ago, without entirely realizing. It was an aluminum-based product, I believe. It turned horrible colors and crinkled up under the glass. 
• I wondered at using silver to do this. I'm told it can work, but my experience with silver stain says it certainly cannot. Ken Leap's book shows an example of firing a piece of solid leaf, and it made a dark amber stain at just slightly higher temperatures than I use to fuse. Further, I've used ground silver leaf in a period formula at much lower temperatures, and it made a light lemon yellow. I'd think 'silver' would necessarily be platinum leaf, which I have not priced or looked at.

Estelle's Vigil: Scarab Platter

EDIT: I've had to do something stupid to get the text to appear on this post. Sorry!

Estelle has, as one of her personal badges, a scarab (dung beetle) pushing a ball of it's preferred element. It's a reference to her peerage theory, quoted here:

The Dung Beetle Theory of becoming a Peer:

First, you gotta find your shit.

Roll around in that shit a while, make sure it's the shit you want to bring home.

Then, you get your shit together.

You gather it up, make it nice and rounded, polish that shit up so that it shines.

Then, you gotta bring your shit home.

So you spend your time, rolling that shit along.  But because you're a dung beetle, you gotta roll it backwards, which means that you really have no clue where you're really headed... but eventually, after a long while, and with a little luck, you get that shit right where it needs to be.

And that's how you become a Peer.

The End.

She requested a scarab platter on which she can serve truffles during her vigil. She provided a design:

We went through available molds and glass colors to find something acceptable:

(There is an invisible piece of clear for the white in this picture. The glass looks slightly hazy -- to me it's as if someone spilled milk on it and wiped most of it off. It was sold as "cloud" and as a translucent white. It wasn't translucent as I would find out...)

I was a bit concerned about how to fire this one. Before I started this piece I had fired one half of the family badge plate (adjacent post). I think it's issues were closely tied to the irregular layering of the glass (2 layers in some places, 1 layer in others). I added more clear pieces to this blank (what I call the piece as it's being fused, before slumping) to try and keep more consistency.

The piece is not perfectly regular, which didn't surprise me. A little grinding fixed that up. There are some unfortunate lines between the body segments, and leg segments. I knew that would happen but I didn't want to overlap the pieces and potentially provoke bubbles. This picture shows how the white striked. I compared it to a piece of "opaque" fusible white, and the piece sold as opaque was actually more translucent than this cloud glass.

With these platters I progressively slid my firing schedule down from 1300 degrees. I think its near 1230 now, with no change in the hold times. I did that to try and avert "dog boning" especially in the square plates. This helpful advice came from the folks at Fused Glass Fanatics on Facebook.

These pictures show the completed (slumped) platter. The actual shape and depth is not conveyed well, I will try to take a better shot next week. The white is clearly NOT translucent. I used my grinder along the edges to make the shape a little more regular and remove some stabby-bits.

Estelle's vigil: Family Badge Platter

Estelle did not ask for this, but some time ago we discussed the idea of making a matched set of platters that, when joined, would form her family badged (used by her whole mundane household). I decided this was as good a time as any!

The plates feature blue bars on a clear (white) field, with green in the corners (skipping heraldry terminology for non-heralds). Because I use a base layer of clear, I didn't see the need to fill in the second layer with clear. This is the first time I've tried any fused project with clear. I expected that the blue might spread or contract a bit, but I thought it would be acceptable:

HUGE bubble. Right beneath the base layer, not between two. The edge was also very irregular. ALSO, the grey sharpie used to tag the glass didn't burn off as I had expected. So, scrapped it and started over.

This time, I added clear layers in the top. The results fused much more smoothly:

And the slumping went well. Initially the shape bothered me, I thought I was seeing the "dogboning" problem I've had in the past with this mold, and I had been correcting my slumping temperature down to try and adjust. After a couple of days I realized they are fine; the molds have a slight curve in a plane I didn't realize, and the shape is closer to the mold's shape than I thought.

The piece in the top of these pictures had some old kiln wash fuse to the glass. For the immediate purposes, this is fine, but I plan to remake it so it has the clarity of the second (bottom) tray.

Lessons Learned:

• Applied kiln wash apparently has a shelf-life!
• Better results with even layer coverage.

"Dogboning"

I enjoy making fused items, too. I made two plates for Their Majesties lunch at Fall Crown last weekend. I had an issue with the first one, and turned to the great people at Fused Glass Fanatics on Facebook.

The "not quite right" but serviceable plate, in the mold.

I was informed this is called "dog boning" and is the result of firing either too quickly or to too hot a temperature. After giving my firing schedule I was told the pre-set schedule I've been using goes about 100°, maybe 150°, too hot. I'm very glad to know this, and to know there is a term for it!

Painted and Stained Award Medallions

[7/1] Their Royal Majesties of the Middle put out a call for award medallions, for ODHs, Evergreens, and Cavendish Knots. Being a guy of one artistic impulse....

I discovered I can drill holes in glass! I knew it was possible, but I've never done it before. A glass bit in my dremel and it was surprisingly very fast and easy.

[7/5/13 Edit] I've got the first coat of color on them, and in the kiln now. I don't know that I care for the cleanliness of the lines yet, but I'm rushing myself. The scales on the Dragon's Hearts are tricky to keep even and regular! The second one looks better because I thought of it in terms of the whole row rather than one scale at a time. That changes how you scrape the line (more like U's rathern than J's if you will) and looks better. The first one:

All six pre-firing:

Paint chips

Paint chip samples, to go into the binder. Before firing they always look lifeless and like drawing pastels, in reflected light:

Pre-firing, in transmitted light. I sketched little phrases on them for contrast. The samples are intentionally not blended even:

This was a very beneficial test, in the end, because the transparent green enamel I thought I bought was opaque. That project got sidelined for a bit as I try to decide whether to try it with enamels, or flashed glass. I don't want a leadline where... ah, but that's another post for another day. Three new colors coming this week to test as well.

Bird Badge Comission

[Now that the weekend has passed and she has the panel, I can post this safely]

I took a commission job from a friend, to be delivered in just a few days. I'm writing this on Wednesday, but I will save the post until the weekend just to be certain the surprise isn't ruined.

The design is her personal SCA badge, a bird bendy blue and white. Unfortunately from a recent remark I don't think this is what she is registering with the society, but the piece is done and her husband, the commissioner, is pleased. [Note: Nope, after she got it she said this was the right one!] I learned a new stupid mistake to avoid while working on this.

The original image provided:

I took a piece of my favorite clear class, a heavily seeded clear, and got to work tracing the design with Reusche stencil black:

Once I got as pleased with the result as an artist can be, I went to fire it. That is when I discovered that the piece of glass I had cut was sized to fit the design I printed out, and not my kiln. For some reason the piece seemed considerably less than the 13" internal space of my kiln, but I forgot to consider it's octagonal shape. After the paint was dry, I had to cut strips off of all four sides to make it fit, and then the corners didn't sit on my round kiln shelf. This lead to my first stupid mistake. I'd been doing a lot of silver stain tests lately and figured that this was safe enough, as this wasn't a slumping schedule I was using.

Unfortunately I was thinking of the 1000° silver stain schedule, when comparing it to a slumping schedule, and not the 1240° to which my vitreous paints must be fired. The next morning I opened the kiln and with horror wondered if I had ruined the kiln.

Not only had the four corners slumped down, two of them resting on the firebrick beneath the shelf, but my careful cleaning of the kiln shelf wasn't good enough. The piece was slumped and picked up residual silver stain, to boot! I got brief amusement recognizing the stained shapes (the Latin cross from Bryan's roundel stands out quite well).The piece was quite ruined and now sits next to my work bench as a reminder.

I cut a piece of glass to fit my equipment and resized the pattern to fit it, and not the other way around. I fired it as before, flipped it over, and enameled it. Another caveat I learned: If you are using a hake or matting brush to remove dust while cleaning up a job, make sure it is actually completely dry. Instead I damaged two of the strips of blue enamel, and had to touch them up. It drives me nuts because you can see the thicker areas on the finished object, but the commissioner had no complaint and time was running short.

I fired it again and the end result was rather nice, especially viewed from across a room:

I've acquired a distrust of enamels, however; the edges of some of the stripes have tiny bubbles that appeared, and otherwise don't seem as even as I would like. Elskus wrote as much in his book, so I expected it. If I were doing it over again I might reconsider and do it with modern copper foil technique and maybe paint the detail lines on as well.

The final piece gets an oak frame and then off to its new owner.

Reusche Stencil Black (RP 1059) (Gum Arabic and Water)



     570°/hr to 1240, hold 0

     Full to 1040, hold 5

     50°/hr to 986, hold 0

Reusche Transparent Blue D2867 (RP D273359) (Gum Arabic and Water)

     570°/hr to 1060, hold 0

     Full to 1040, hold 5 [I typically use the same schedule for my enamels and vit. paints, just changing step 1]

     50°/hr to 986, hold 0

Oak framing stock (1" x 3') from Delphi. Hardware from local hardware store. Base glass unsure, I get it from a local shop and  love it. It's one of the cheapest clears I've seen, which does not detract from the fact it's one of my favorites.

Memorial Disks

After several weeks of not being able to stand at my work benches (sprained ankle followed by gout attack), and with very few weeks until my last option to enter MK A&S for the year, it's time to put the hammer down and get serious, or I won't be entering this year at all.

It took a dozen tests to get everything settled, to get a method to create two armorial disks. The disks are bearing the arms of a departed friend, blazoned "Azure, a chevron argent, overall a Latin cross Or." One will go into a panel for A&S. One will be attached to the lid of the handmade box containing his ashes.

I ordered two square feet of flashed glass, blue-on-clear. I also had a small (7x7") scrap of blue I found on a fluke at a local shop that doesn't normally carry flashed. I placed that into my Morton circle cutter and popped out a perfect disk. For the second disk, I cut one of the new sheets up. Popped it into my circle cutter, and met with heartbreaking (and expensive) disaster as the disk mis-cut. A second square became two more half-circles. Then a third. I blew through $75 worth of glass in an hour. I decided to forgo the fancy circle cutter and do it slowly, by hand and grinder.

Not too bad. Then, on to the acid etching. Resists/masks have been a problem for me, after several tests. Duct tape (fuzzy edge), contact paper (very fuzzy edge), and a resist gel were tried and found problematic. Most of the "tape" solutions I was trying are actually suggested for sandblasting flashed glass, not acid-etching it. I tried them anyway, because I had no better ideas and I'm not yet equipped for sandblasting. The gel was especially tricky because after I smeared a coat on the glass, I needed a "resist resist" to keep clear my target pattern. I laid down duct tape first, and lifted it to try and leave behind what I needed, but the lines weren't clear enough for my taste.

I ended up going back to duct tape, figuring I'd rather have a roundel with slightly fuzzy edges than none at all. I wanted a wider roll, however, to avoid issues where two pieces of tape match. A trip to the hardware store turned up a 4" wide roll of Gorilla-brand tape... and this stuff is mighty. I put a strip of Gorilla tape mostly across where the design will be, and two extra strips above and beneath. I then covered the gaps with two more thin strips, trying to get as much coverage as possible. I put a copy of the roundel on top with white glue, attacked it with an X-Acto knife, and got something workable.

Then, began the cycles of acid etching cream. Five of them, I do believe, in all. Sitting on scrap mirror for protective purposes:

After two coats, I believe:

Three coats:

 

After four:

 

I was shocked but pleased with the result. I gave it a fifth coat to clear up the edges. The glass is a lot clearer than I expected, more so than with sandblasting. While washing it in the end the water filled in the pits and made it completely clear.

The Gorilla tape worked far, far better than I had hoped. It stood up to wirebrushing to remove dried coats of acid etch, and kept the fine points intact. Here is a shot on top of my ancient crown template, for visibility.

Now knowing how to get the silver stain to work, I applied my stain and fired it.

I am exceedingly pleased with the result!!! Now, to get it into a panel....

Painting Practice Pieces

I made a quick practice piece to check my firing schedules and the paints:

For some reason (other than being an SCA herald?) I like to use an Ancient Crown for my practice pieces. I mixed a small batch of Reusche 1059 tracing black, and a matting color of about 50/50 Reusche 1220 A gray green and 1110 bistre brown #7. I did the matte, waited, very roughly traced the ancient crown, waited. I removed the matte from about 2/3 of the crown and did a thin highlight around the entire border. Fired it, applied the silver stain, tried a new blender, and fired. This shot shows some of the matting coming off:

 I'm using Reusche 1384 silver stain, Yellow #3. I had a previously mixed batch. I took a small bit, diluted with lavendar oil, and diluted it too much. Then I kept putzing about with it, and it was too dry when I went to hit it with the blender. Eh, I thought, it's a test piece. Fired it again:

 I am not unhappy with it. The matting is too light, the lines irregular and poorly traced (but it was a test piece), and the silver stain uneven. The only actual problem I've noticed is metalling where my silver stain is thicker. It happened once before, as well:

 

I checked my firing schedule (I'm using schedules from Williams & Byrne), and I noticed that my current schedule only goes to 1040°. Metallizing, as I understand it, normally happens when you fire too hot. RP 1384/Silver Stain, Yellow #3 has a listed firing range of 1050-1080. I'm going to do two more tests this week, firing to 1020° (20° below my current schedule) and 1060° (20° above) to see what the effects are. Viewed directly on the stain is pretty, this may be something I end up having to live with, because I can't image 30 degrees below the listed range is going to make it better, and going higher should make it worse if this is actually metallizing.

(Update, 4/17/13)

I ended up with interesting results. The test piece fired to 1060°, just inside of the manufacturer's listed range, turned out horrifically bad. I went ahead and fired it on a chip with a blue enamel I have plans for, and this was my result:

Horrible metalizing, "yellow mother-of-pearl" as I expected from Williams & Byrne's books, their description of overfired silver stain. It looks horrible in both reflected and transmitted light.

The chip fired to 1020° was relatively the same as 1040°:

Looking straight through it, its functional, but there are some off spots and in reflected light you can see its still not right. Thirty degrees beneath the listed range, and it's still not right? I started to suspect I was firing for too long, then, because surely it couldn't be too hot...

Checked Elskus, seeing what he had to say on the matter. Silver stain, according to him, has a functional range of 950° to 1050°! I'm still on the high end, according to him. Ok, one more chip, at 1000° then.

This picture doesn't do it justice. Beautiful and quite even. I stared at the chip for several minutes, held it up to various lights, placed it on my lightbox. I put it by my computer and picked it up ever few minutes for an hour, staring. 1000° it is, then, and that temperature has been working great for me. As the masters wrote and write, experiment and experiment some more...