The unity formula is the molecular ratio of the elements in a particular glaze. Those elements are supplied by the raw materials in the glaze recipe. The unity formula allows us to compare glazes more accurately than looking at a recipe, since a glaze with 15% calcium carbonate by weight in the recipe isn't necessarily 15% calcium in it's final fired state. Also, many materials supply more than one element, so the unity formula shows that. The unity formula also allows us to substitute materials, since there are numerous materials that can supply each element. It also allows us to make specific changes to the glaze that can't easily be made by changing the raw materials in the recipe.
Example: I have this glaze that I love, and I use it all the time. The recipe contains materials that are all mined here in the USA. If I move to Australia, I won't have access to those specific raw materials any more, but I will have access to other materials that can supply the necessary elements to make that glaze. So I can take my recipe and convert it to the unity formula, then convert it to a new recipe using the materials I have available. The recipe is different, but the molecular makeup of the glaze is the same.
Another example: I need to increase the alumina content in a glaze. There's no alumina in the recipe- it's being supplied by the feldspar and the kaolin. If I increase the feldspar, it will also increase the potassium and sodium and silica. If I increase the kaolin, it will also increase the silica. So I have to go into the unity formula, increase the alumina in the formula, then convert it back to a recipe.
The Orton datasheet says "as a general rule, a 1 to 2 hour soak is sufficient to deform the next higher cone number." so I was expecting 20 minutes to only make a small difference, perhaps only 1/2 a cone.
I've done a number of soaking tests in my electric kilns, and combined with that experience and everything I hear about here on the forum, the degree to which soaking affects cones seems to be very inconsistent. I used to fire my big electric to cone 6, then soak for 40 minutes to achieve cone 8. Much shorter than the 1-2 hours you mention from the Orton sheet. When I started firing cone 6, I tried a similar soak to go from cone 4 to 6. It took 80 minutes, and the glazes did not respond well at all. Many were under-fired. And every couple of weeks here on the forum we hear about someone's kiln that accidentally soaked for several hours, with surprisingly few poor results. A couple of pots stick to the shelves, but by and large things seem to survive. Soaking is a strange thing, and while short soaks (under 20 minutes) seem to have noticeable affects on glaze melt, as the soaks get longer the effects seem to diminish. It seems that at some point you need higher heat, not just heat work.
Just my thoughts, which may or may not be at all accurate.
I would do away with the box plugs and just hard wire the sections together with slip-on terminal connections. Those plugs are a weak point in the system, and will fry out in the (near) future. Replace all the elements, and any bricks that are broken.
It will depend on what size the kiln is. At 22 amps, it shouldn't be any larger than 18" wide by 18" deep, and even then it's ever so slightly underpowered. Most modern kilns of that size pull 24 amps. But you should be fine getting to cone 5 as long as the elements are good.
Neil. I know this has been posted before but can you give the cooling ramps from C 6 to accentuate this. I think you posted something about when you do a soak on the way down but I can't find it with my searching.
Now firing the kiln with controller and this is may come more easily to my repertoire now I hope!
I cool at a rate of 175F/hr down from peak temp to 1550F. Many people let it crash cool down to about 1900 before starting the slow cool, but I do it from the peak so that I get the same results in all 3 of my kilns, which will crash at radically different rates. Some folks also go as low as 1400F, but I have not seen any difference in my glazes below 1550F. I've tried cooling at rates below 175F/hr, but some of my glaze come out too matte for my liking. I would start at 175F/hr and go from there, reducing the cooling rate in 25 degree increments. You could also try adding a hold at around 1900 and see how that affects things.
It has to do with crystal growth. If you soaked the kiln at low temps you could get a similar result. Slow cooling an iron red will increase its redness, for instance. When you refire to the same temp, things change because the melt is different than the first time. Refires will tend to melt at a lower temperature, and things may get melted better than the first time with the additional heat work.
Porcelain should not have any impurities- that's the nature of porcelain. The problem with crawling is probably because the thin rims get too saturated when dipping the glaze, which prevents good adhesion. Try glazing the inside first, clean off any overrun on the outside, then letting it dry overnight before glazing the outside.
That appears to be a fairly rough clay, and you can see from the closeup photo of the name stamp that there's a lot of unevenness below the glaze surface. This spot was probably an impurity that burned out in the glaze firing or a bloat. Either way it left a void. Eventually the thin glaze layer covering it gave out. Since it's not on the inside where food touches it, I would just leave it unless it will tend to get filled with food and gunk. I would I don't think there's any reason to believe that it will cause a huge crack or anything like that, though. Epoxy putty will fill it nicely, but to to do it cleanly while the putty is wet so you don't have to do any sort of grinding or scraping which could ruin the glaze. Use a marine grade epoxy that will hold up well when wet. The repair will be visible, but that's okay. It's a sign of use and love.
Here's a series of photos showing how I pack a lidded vessel for shipping. The whole idea behind this is to create a double box type of package without actually using two boxes.
First I prepare the pot by putting a couple of layers of thin foam packing material between the upside down lid and the pot. Then I cover the piece with either bubble wrap or paper, whichever I have handy, and tape it up tight so the lid can't move. The bubble wrap/paper is just there to keep the tape off the pot. I do not ever use bubble wrap as a packing material. It's overpriced, and you have to use many layers of it for it to be effective. Foam sheets are cheaper, and do a better job of protecting lips and edges.
Then I put 3 inches or so of packing peanuts in the bottom of the box, followed by a sheet of cardboard. This, and all of the cardboard pieces I will be using, are there to keep the pot from migrating though the peanuts as the package gets jostled about in the shipping truck, as well as provide another layer of protection.
Then I start adding peanuts. Once they reach about halfway up the pot, I put in the side baffles. Again, these provide a big flat surface that can't migrate through the peanuts, ensuring that the pot stays centered in the package.
Then I add more peanuts above the top cardboard baffle. Notice how they are mounded up higher than the box. This is so that I can compress them down as I tape up the box, so everything it nice and firm. During shipping the peanuts will settle a bit, so if they're not packed in super tight you'll end up with a loose packing job. Movement is what breaks things during shipping. If nothing can move, nothing will break.
The only way to add it to an electric kiln would be to get it between the bricks and outer jacket. You'd have to get a longer jacket to accommodate the added thickness, and you'd have to use fiber board which doesn't compress, not kaowool. But even when done at the factory I find it to be a big mess. I hate working on kilns that have the extra insulation, and I have yet to see any real numbers to back up claims of substantial energy savings. There have been several discussions about this here on the forum. Do a search and you'll get a lot of info.