I think handmade plates and platters should be as thin, or at least close to, as commercial plates and platters. Unless they serve some special function where they pretty much just sit in one spot for a long time, they need to be thin so that they aren't annoying to use. I want to be able to lift 4 to 6 plates out of the cabinet at a time when setting the table. I want them to fit between the dishwasher tines easily. Just because they are hand made doesn't mean they shouldn't function every bit as well. There's not necessarily a specific thickness I shoot for, but if I pick it up and it feels too heavy, it needs more trimming.
Firing to cone 6 will max out that kiln, which means it will fire pretty slowly at the end, which also means you're wasting a lot of electricity. Typically you want a kiln that will fire 3-4 cones higher than what you'll be firing to, so it will have plenty of power to meet your firing schedule. By maxing it out, you're at the mercy of the kiln when it comes to setting the schedule at the high end of the firing. And when the elements start to age even a little bit the kiln won't be able to reach its max. If it was rated to cone 10 and you were firing to cone 6, you could get away with firing on older elements because you're not at its peak.
Many 120 volt kilns are underpowered, and yours is only a cone 6 kiln so it's even more underpowered than a cone 10 version. At a cone 6 rating it really shouldn't be fired higher than cone 3. They need everything working properly in order for them to function correctly. At 8.8 ohms your elements are 10% off from the factory original, which is exactly the amount of wear when replacement is recommended. Assuming everything else it working properly (thermocouple, relays, etc) then it's probably the elements causing the problem.
Test it out and see what you think. It may or may not be a problem. If needed, reformulate for whatever you have access to, be it Gerstley or Frit. Frits do not settle badly if you have a well formulated glaze with enough clay to keep it suspended. The problem is that a lot of old glaze recipes relied on Gerstley to keep the glaze suspended, which it does very well. So if you substitute a frit in those cases then you can have suspension problems.
It is extremely rare that you would need to deflocculate a glaze. Usually if it's too thick you just need to add water, which seems to be the case here since they have sat around for a long time. If they settle out too quickly or too hard, then you need to flocculate with epsom salts.
The holes should work fine if you're using a long leaf loose tea, which most North Americans don't. I was taught to glaze a teapot with a built in strainer by lining the interior, and before the glaze sets up, blow the excess glaze sharply back down the spout so the holes are all clear. It's much less hassle than messing around clearing the holes with a brush/pipe cleaner/whatever, or getting them all wet beforehand.
All of that said, one large hole works just ducky.
In my experience, with small holes the glaze will set up and plug them before it can be blown out, especially with porcelain which takes in water quickly. And with runny glazes like I use the holes will fill up during the firing, so a thin layer of glaze is necessary, which wetting the holes before glazing accomplishes. It only takes a few seconds to wet them with a floppy brush.
To keep small holes from filling in with glaze, wet the holes with a brush before glazing. Because the clay is already saturated it won't take in very much glaze. Immediately after dipping the glaze, blow through the spout to clean out the holes.
What is different about porcelain that makes it stick together when fired to ^6? Can it touch during the bisque? Would unglazed stoneware stick together if fired to ^6?
I was very surprised to learn this. Thank you again for your experience and expertise.
Porcelain gets very close to its melting point, therefore pieces stick. Think molten glass. Stoneware not as much, but still sticky to some degree. In a bisque it's not a problem because the clay doesn't get anywhere near its melting point. You could stack raw pieces in a cone 6 firing, but you would need to do some alumina wax wherever they touch, and they're much more likely to warp if you stack them.
First, burning duct tape is not a good thing. It's plastic, so the fumes are not going to be nice. As for the volume of paper, the vent won't be able to handle it. You won't necessarily do any harm to the kiln or vent, but you're going to have a lot of smoke coming out of the kiln. Downdraft vents just aren't made to handle that kind of burning out. I've had calls from more than one school who set off the smoke alarms trying to burn out a lot of newspaper. When using newspaper forms, they should be loosely packed, using as little paper as possible so that the paper can compress as the pieces dry and shirnk, and you should remove as much as possible before firing. I would try to figure out a way to open up the pieces and remove the paper, or figure out a way to vent the room when the kilns starts smoking.
With vitrified clay the alcohol cleaning shouldn't be a problem. I would think that even with porous clay the alcohol would evaporate out. Keep your clay under 2% absorption and you should be fine without glaze. Wood pipes aren't sealed on the inside, are they?