Overglaze

So I'm using some glaze from Duncan Ceramics. I screwed up of course. The directions said:

1. Apply to shelf cone 04 bisque.
2. Fire to shelf cone 06.
3. Clean up with water.
4. For clear glaze application, brush-on or dip clear glaze over Concepts.
5. Stilt and fire to shelf cone 06.
6. Water clean up.

Somewhere in the course of reading stuff, I stumbled upon something about matte or flat underglazes. I made the wrong assumption that all of them are matte. So then it made sense to fire it, apply the clear glaze, then fire it again 2 cones lower.

Well, not so much.

With this system the clear glaze is supposed to go on before firing. Fortunately the underglaze is also OK to fire alone. So the bowl was not wasted.

John

Cone 04 Firing

Started today at about 11:00 a.m. with the Cone 04 firing. 7 hrs. and 10 minutes later, about 6:00 p.m. the program ended. The cone was just above the shelf and the temp was at 1945 degrees F.

So I am concluding that the thermocouple is properly calibrated and the program is about right. I'm actually very impressed that they wrote these programs so they hit the cone energy values as close as they did.

It's 9:00 p.m. and the temp is down to 618 degrees F. At first is dropped 600 degrees + in the first hour, then slowed. I used to know the formula for this. The rate is logarithmically related to the difference between the temperatures I believe.

The picture here is at the beginning of the cycle. I kept the lid cracked for about 90 minutes. As it approached 500 -600 degrees F I noticed some burning like smell coming out. So the glaze gases something as it gets hot.

I had some trouble positioning the cones. I thought they would be OK. The pictures here show them before I started.

Oh, it rained a little today. The work around is working OK. I discovered I need something like a porch roof. So I need to extend the roof about two feet. I think I'll do this with a light weight 1 inch square tube instead of the 2 inch square tube.

The final solution is going to be an elevated floor in the shed. There's plenty of room for that. That'll make it as weather proof as any building.

Later,

John

Kiln & Rain

The enclosure worked OK but not perfect. There was quite a bit of spatter from the bottom side openings. I did not anticipate it would get in that far or that high. So the bottom of the kiln and the control box were wet.

I'm heating it up to 200 degrees F now and will hold it for a couple hours at that temp. Then I'll try it at like 500 degrees to see what we get.

The temporary fix is to put some aluminum sheet scraps around the bottom to stop the spatter from the falling rain. I'll probably get some magnets to hold them on and cut them to fit tomorrow. Should do the job. That way I can adjust them to still allow air in the bottom.

Later,
John

Cone melted

Not sure if this is normal or not yet. My wife told me that the cone bent all the way over. When I looked at it in the peep hole I swear it was not bent over yet. I read something about them bending after soaking for a while. So, I wonder if they are just always going to bend and the real measure is the point at when they bend to whatever angle at first. Then they just keep bending. For some reason I got it in my head that they stopped. But that doesn't make sense now.

So Saturday morning I head back over the Aardvark to get some 03, 04, 05, 06, 07 cones. I have a bowl that's coated with glaze. I want to fire it to an 04, then put the clear coat on it and fire it to an 06. I'm planning on using the medium ramp rate just for consistency in testing. The glaze is supposed to be a really dark blue. Hopefully it comes out OK 'cause it's a nice size for an Oatmeal bowl.

I think my wife wants to do some plates too. I think with some additional shelves we can do four plates at once in the kiln. So this should be fun.

Later,

John

Kiln at 868 degrees

So the kiln hit 2030 or so degrees at about 9:15. I had to shut it off. I think it should have shut itself off, but I'm not sure. There is some difference between the cone types and the temperature they bend at. The cone had not bent at 2030. So ... this will need to be tested again. This time it will be at cone 04 which the chart shows at 1915 to 1971 degrees. That'll take less time and I want to fire a glaze next time. The glaze I got is a cone 04 glaze.

http://www.ortonceramic.com/resources/pdf/wall_chart_degreeF.pdf

Need to figure out where the computer runs relative to the chart and if it compensates for heating rate. Oh, this was all at the medium or standard heating rate.

It's about 1:15 a.m. now and it's down to 868 degrees. No longer glowing inside.

The front of the control box probably got up to 150. The shed stayed cool to the touch actually. The top of the shed was warm, but not at all hot.

Good night.

John

Kiln Firing Update

It's about 4:00 p.m. The kiln is at about 1850 degrees. It is starting to glow inside. The outside is now too hot to touch. I don't have any way to measure how hot it's getting. By the way this is a Paragon Janus kiln. The little one.

http://www.paragonweb.com/JANUS1613.cfm

I checked the current at the panel. It's pulling 19.12 amps on each leg. I calculated 18 amps based on the specfications. The resistance of the coils must be a little lower than specified. Well, I need to rerun my math. I think I used 220V. I measured my voltage at 240V using a wiggy. Which is not a real accurate device. So perhaps I should measure the voltage and recalc.

Nothing odd is happenning. It appears to be heating up nicely and in a very controled fashion.

Later,
John

First Kiln Firing Begins

This morning, I made it over to Aadvark in Santa Ana and picked up some cones, a greenware bowl, some blue glaze, and some clear glaze. Mis-read the kiln instruction which said to get 01 cones. I got 1 cones. Still getting used to this.

The cone range is from 022 to 14. It goes 022, 021, 020,...,03, 02, 01, 1,2,3,..., 13,14,15. Kinda wierd. More wierd than wire sizes even. Fortunately the temp difference between a 01 and a 1 is only 30 degrees. So I'm going with it.

I applied the kiln wash to the bottom and the shelves. Mixing this up was easy. It's a fine powder. Make sure you use your N95 dust mask! Just put some in an old butter tub, added water, and mixed with a cheapo throw away brush. I used about a 1/3rd of the bag Paragon sent with the kiln. They said mix it to a consistency of thick cream. I'd say uncut latex paint was closer. Maybe bar-b-q sauce or ketchup. The shelves were thirsty. The kiln bottom was less thirsty than I thought it would be. On the shelves is seemed to be better to get a good glop on there and spread it pretty quickly across the shelf. I was using a 1 inch brush. A 2 inch would have been better actually.

So, it's about 1:00 p.m., it's been on for an hour and is approaching 400 degrees.

It comes on and goes off in about 10 second increments. So it's probably actually a 50% duty cycle. That's very good for the wiring. I now feel a heck of a lot better about the safety margin of the electrical specifications.

More later.

John

Electrical run. Kiln has power

So I got the electrical done today. Put on the shed roof vents and moved the kiln up from the garage. It has been plugged in and I have seen the "Idle" word on the LED panel. Which is what I am supposed to see. Yay!

Success! This has been a long and much interupted project.

Correction on the plug. It was supposed to be and L6-20. I bought the wrong ones. That has been corrected. This is pretty important. The L5-20 will allow a regular 120V plug to be plugged into it. That would spell at least a blown fuse on something, probably ruin whatever you plugged in, and possibly end up with a fire. All bad things. So, the L6-20 will not allow this. One would have to replace the plug on the 120V device. Unlikely and if one did that serves you right I suppose.

I need to supply a more organized and detailed write up of what was done. Here's the recap.

• Built a metal shed for the kiln from scratch.


• Filled in the bricks on my patio so I had a place for everything.


• Provided a 240V sub panel and extended the circut to a plug near the kiln.


• Set up the kiln.

Sounds simple when I put it that way!

Later,
John

Electrical so far ...

No wiring today unfortunately, but I got most of the conduit run. I was all over the place today. ADD! Seriously. Anyway. The sub panel is mounted, the ground rod is in, the conduit between the air conditioner and the sub panel is hooked back up, the conduit between the sub panel and the future home of the 520-R outlet is run.

The conduit between the breaker box / sub panel and the box where the feed comes from needs to be run, the box for the 520-R receptacle, and the wiring needs to be done in the a.m. A few clips for the 3/4" EMT need to be put up too.

This was my first shot at bending EMT. EMT is short for Electrical Metallic Tubing. There are two kinds of metal conduit that you most generally see EMT and Rigid. Rigid is like galvanized water pipe, except the plating is cleaner. EMT has a much thinner wall and can be bent with a hand bender. I bought a new one today.

This is one of those things you can rent but for only $40.00 to buy you are on the border of paying for it if you rent it. It's probably $10.00 a day or something plus your time and fuel and pain in the back side factor. I will use it again in the shop too. Besides, why pass up a good excuse to expand the tool collection? ;-)

Surprisingly I only goofed up one piece of EMT doing the bending. This was my first attempt at doing it ever, so I was pretty happy with that. I'll have to see if I can explain how that works in my next posting.

So, maybe tomorrow, or later today as the case seems to be, the kiln can be test fired.

Later,
John

The Kiln Project

The Kiln project continues on today. The shed, or Dorothy's House as we are calling it, is done. The electrical work is on tap for today. Pictures to follow. Then you can see what the Dorothy thing is about.

I have a two circuit sub panel I am going to put in the 220 V single phase line for the A/C. The A/C line is OK at 30 amps. The Kiln pulls 20 amps. Actually I think it pulls 18 amps max. This is equivalent to four blow dryers. So, not that scary. It's not small however.

Once hooked up I will measure it with the amp clamp and see what the truth is.

I've had more power going with a bunchof halogen work lights to be honest. So been there and nothing has burned down so far. But, better safe than sorry.

So, I am putting 30 amp breakers in the sub panel. The kiln leg will be turned off unless it's being used and then I will shut off the A/C. The plan for summer is to run the A/C at night to get the house chilled, then fire up the kiln early. High fire duration takes like 12 hours. The A/C can probably be turned back on during the cool down leg which is about the last 1/2 to 1/3 of the cycle.

I need to measure the draw during cool down and the draw of the A/C compressor. I suspect both of them together during the intermittent cool down ramp time might bo OK. We'll see. It will depend on how long the kiln coils kick in to keep the ramp cool down rate OK.

Also, as shipped this kiln has one thermo couple. So, when it goes on, all the coils go on. Adding two more thermo couples might lessen the amount of time all three coils are on at the same time. I would expect the lower coil to run more and the top coil to run less.

Slower cool down ramps equate to structurally stronger ceramics, I think. Less cracks anyway.

Later,
John