Jeff Longtin

A variant of this: my studio is filled with a few porcelain pots, but its packed full with plaster forms on their way to becoming plaster casting molds. Most people, even other clay people, can't distinguish between a porcelain pot and a plaster form. (Especially now that I'm using matte glazes.) Visitors to my studio regularley express an interest in buying my plaster forms. When I explain that it is part of the mold making process they usually say, "I don't care, can I buy it." 

I certainly didn't think glazing the pieces would be so complicated. I thought about spraying the glazes, for uniformity, but that too has complications.
Here's another photo showing more color tests.  Each of these test tiles represents a Mason Stain that no longer is being produced. The far left tile features Robins Egg 6 with Delphinium 2. The next tile is Delphinium 1.6 with Zircopax 8.4. The intense blue is Delphinium at 3.5% and Zirco 2. The purple tile is an attempt at the Violet and Amethyst. (6001 Pink with Vivid Blue)
The two yellowish tiles represent Peach. (6001 with Praesadium Yellow.)  
Note:  Many years ago Mason sold over 200 different stains. Today they sell 80-90. (guessing) They decided the world probably doesn't need to 10 different types of purple. What they did, instead, is to post the recipes for those discontinued colors on their website. ("Archived Formulas") Its tedious buying several stains, to produce one, but it does lead to some surprising color variations.

As this just came out of the kiln I thought I would share: these are cone 6 porcelain casting slip test tiles.  (Coasters cut in half.) To which I've added various amounts of Mason Stains: Vivid Blue, Delphinium Blue and Zircopax. 
So that I can apply the glaze thinly I add stain to the clay, as well, to add to the opacity of the glaze. (I find that glaze drips/overlaps, become less evident if the clay body matches the glaze.)
Rather than use a total amount of 6% Vivid Blue, in the glaze, on top of a very white porcelain body, I added 3% to the body and 3% to the glaze. 
Its been a tedious process but its really interesting to see how the stains interact with the clay and glaze.

I certainly didn't think glazing the pieces would be so complicated. I thought about spraying the glazes, for uniformity, but that too has complications.
Here's another photo showing more color tests.  Each of these test tiles represents a Mason Stain that no longer is being produced. The far left tile features Robins Egg 6 with Delphinium 2. The next tile is Delphinium 1.6 with Zircopax 8.4. The intense blue is Delphinium at 3.5% and Zirco 2. The purple tile is an attempt at the Violet and Amethyst. (6001 Pink with Vivid Blue)
The two yellowish tiles represent Peach. (6001 with Praesadium Yellow.)  
Note:  Many years ago Mason sold over 200 different stains. Today they sell 80-90. (guessing) They decided the world probably doesn't need to 10 different types of purple. What they did, instead, is to post the recipes for those discontinued colors on their website. ("Archived Formulas") Its tedious buying several stains, to produce one, but it does lead to some surprising color variations.

As this just came out of the kiln I thought I would share: these are cone 6 porcelain casting slip test tiles.  (Coasters cut in half.) To which I've added various amounts of Mason Stains: Vivid Blue, Delphinium Blue and Zircopax. 
So that I can apply the glaze thinly I add stain to the clay, as well, to add to the opacity of the glaze. (I find that glaze drips/overlaps, become less evident if the clay body matches the glaze.)
Rather than use a total amount of 6% Vivid Blue, in the glaze, on top of a very white porcelain body, I added 3% to the body and 3% to the glaze. 
Its been a tedious process but its really interesting to see how the stains interact with the clay and glaze.

Welcome to the forum Liat. Most potters I know use plywood boards as well. 3/4" usually. To pick up on Mark and Kelly's point: I would say its mostly about allowing your boards to dry at some point. Rotating them might reduce/eliminate the problem. Not sure what constitutes "cheap plywood"?  Are you referring to particle board? (composite board) The first boards I used were particle board. For some reason the surface would become raised and pebbly, after a pot sat on it for a few days, so I tossed those and went with plywood instead.

As this just came out of the kiln I thought I would share: these are cone 6 porcelain casting slip test tiles.  (Coasters cut in half.) To which I've added various amounts of Mason Stains: Vivid Blue, Delphinium Blue and Zircopax. 
So that I can apply the glaze thinly I add stain to the clay, as well, to add to the opacity of the glaze. (I find that glaze drips/overlaps, become less evident if the clay body matches the glaze.)
Rather than use a total amount of 6% Vivid Blue, in the glaze, on top of a very white porcelain body, I added 3% to the body and 3% to the glaze. 
Its been a tedious process but its really interesting to see how the stains interact with the clay and glaze.

I'll share another aspect to the bisque temp decision: thinness of the clay piece.  Using the process of slip casting often results in a clay wall that is thinner than thrown pots. (Especially porcelain.) Firing to cone 06 can result in a very absorbent pot. Sometimes this overly absorbent clay wall can absorb too much glaze. (Crawling can result.)
Firing to a hotter temp, 05 or 04, reduces the absorption and makes it easier to get a thin glaze application.

As this just came out of the kiln I thought I would share: these are cone 6 porcelain casting slip test tiles.  (Coasters cut in half.) To which I've added various amounts of Mason Stains: Vivid Blue, Delphinium Blue and Zircopax. 
So that I can apply the glaze thinly I add stain to the clay, as well, to add to the opacity of the glaze. (I find that glaze drips/overlaps, become less evident if the clay body matches the glaze.)
Rather than use a total amount of 6% Vivid Blue, in the glaze, on top of a very white porcelain body, I added 3% to the body and 3% to the glaze. 
Its been a tedious process but its really interesting to see how the stains interact with the clay and glaze.

I'll share another aspect to the bisque temp decision: thinness of the clay piece.  Using the process of slip casting often results in a clay wall that is thinner than thrown pots. (Especially porcelain.) Firing to cone 06 can result in a very absorbent pot. Sometimes this overly absorbent clay wall can absorb too much glaze. (Crawling can result.)
Firing to a hotter temp, 05 or 04, reduces the absorption and makes it easier to get a thin glaze application.

The pottery shop most associated with this process is Dock 6. Kerry Brooks is the potter and she applied this process to coasters as well. She spent a year, or two, developing the process and the glazes that go with it. 
Again, she spent a year, OR TWO, developing this and I know she had a lot of failures. (Her studio/shop is a few miles from mine. I know she experimented with glazes, with firing temperatures, and with types of glass.)
Once she found success technically she found success in the marketplace. (Anthroplogie ordered 1000's.) 
Having seen failed experiments with coke bottles, in high school and college, I have never felt inclined to attempt anything like this. She found the sweet spot and her coasters really are a thing of beauty.

From very cold/snow bound Minneapolis:
You have two options: 1) find a matte glaze that works for you OR 2) simply leave your piece unglazed and use underglazes. 
1: white color, in a glaze, is achieved by using a white color or opacifier.  Zircopax is both. It's also cheap. It does, however, have a slight ivory color to it. That it why its often coupled with a truely white material, Mason Stain White 6700 or tin oxide. The Mason Stain is about 2x the cost of zircopax and tin oxide is on par with cobalt these days. (very expensive) Both of these additives are a bit "whiter" than zirco (its subjective I would say) but owing to the expense are usually used to boost the zirco and not used outright. Something like 8% zircopax and 2% 6700 or tin could be a good starting point.
2: the Amaco underglazes, fired to glaze temps, would give you a very DRY surface if thats what you're looking for. The LUG version is more zircopax like, in appearance, and the Velvet version is a much colder white. Apply three coats, with a brush, and you should have a nice opaque color.  (I usually like to thin the first coat so it brushes smoothly.)

The pottery shop most associated with this process is Dock 6. Kerry Brooks is the potter and she applied this process to coasters as well. She spent a year, or two, developing the process and the glazes that go with it. 
Again, she spent a year, OR TWO, developing this and I know she had a lot of failures. (Her studio/shop is a few miles from mine. I know she experimented with glazes, with firing temperatures, and with types of glass.)
Once she found success technically she found success in the marketplace. (Anthroplogie ordered 1000's.) 
Having seen failed experiments with coke bottles, in high school and college, I have never felt inclined to attempt anything like this. She found the sweet spot and her coasters really are a thing of beauty.

The pottery shop most associated with this process is Dock 6. Kerry Brooks is the potter and she applied this process to coasters as well. She spent a year, or two, developing the process and the glazes that go with it. 
Again, she spent a year, OR TWO, developing this and I know she had a lot of failures. (Her studio/shop is a few miles from mine. I know she experimented with glazes, with firing temperatures, and with types of glass.)
Once she found success technically she found success in the marketplace. (Anthroplogie ordered 1000's.) 
Having seen failed experiments with coke bottles, in high school and college, I have never felt inclined to attempt anything like this. She found the sweet spot and her coasters really are a thing of beauty.

The pottery shop most associated with this process is Dock 6. Kerry Brooks is the potter and she applied this process to coasters as well. She spent a year, or two, developing the process and the glazes that go with it. 
Again, she spent a year, OR TWO, developing this and I know she had a lot of failures. (Her studio/shop is a few miles from mine. I know she experimented with glazes, with firing temperatures, and with types of glass.)
Once she found success technically she found success in the marketplace. (Anthroplogie ordered 1000's.) 
Having seen failed experiments with coke bottles, in high school and college, I have never felt inclined to attempt anything like this. She found the sweet spot and her coasters really are a thing of beauty.

I’ve been using neodymium magnets as glazing tools too, thanks to @Min suggesting this to me several years ago. Can confirm that this is a game changer! I have my inside magnet wrapped in fabric held on by a rubber band. The fabric helps cushion the magnet so it doesn’t disturb the liner glaze, and the rubber band “stem” is like a handle. My outside magnet has a big eye bolt as a handle. 
I’ve learned to keep them stored on two different shelves, otherwise they will seek each other out and stick together, and it takes a lot of strength to pry them apart! 

Glazing tools and tips brought up in this thread, starting a new thread as this should probably be in the Studio Operations section.
This is how I use magnets when glazing, no tong marks, drips or finger marks on the glaze. It’s been a game changer for me with the pots I dip. Flat bottoms on pots work the best but you can do rounded bottoms, it’s just a bit less stable while dipping. 
- liner glaze the inside like usual
- rare earth magnet(s) wrapped in a scrap of plastic with twist tie inside the pot. twist tie is used as a handle. keep the twist tie below the rim of the pot
- another rare earth magnet(s) with a flat head bolt for a handle on outside of pot
- fishing magnet used for larger pots, they come with a handle so don't need a flat head bolt for a handle
-number of magnets needed determined by pot weight (and base thickness). I try to use just enough to be adequate to pull the pot from the glaze but not more or else they can be fiddly to remove. for tiny pots I use 1/2 pieces of broken magnets.
- hold the pot by the bolt and push the pot into glaze then lift it out. (rotate the pot slightly to have any excess glaze roll around the rim) 
- when the pot is dry enough to touch at base area turn it over and remove magnet(s) from either side. 20 seconds or so for most glazes. I hold the pot on the outside bottom of the pot when flipping over 
- you can slide the pot onto the edge of a counter while removing the outside magnet if you don’t want to wait for the glaze to dry enough to hold onto the pot, or stuff your hand inside the pot to move it to a ware board.
- when I first started glazing like this I got a couple blood blisters, don't pinch your fingers, those magnets are strong!!!! I use the ones from Lee Valley tools. (to separate them use an edge of a counter and push them apart)
Anyhow, that’s it, simple and it works. I tried to think of a way to market the magnet glazing but life got in the way.

Lots  of pix at https://tinyurl.com/2rkyb27z ... two  particularly lo-tech ones are

It would be interesting to know if  "fingerdips" work
Use a car dent puller to dip your pots in glaze! https://tinyurl.com/2p9y6bn3\\\\\\\\\\
Apparently suckers can be useful in some circumstances

Parmesan jar lids have holes already!

Here are plate tongs made from plastic jar covers. (For some reason the image is sideways?) The many holes prevent the lids from holding glaze which then drips onto your still wet plate. The little notches in the lid rim aid in holding the plate edge. Once the glaze is dry I dab a little glaze where the lids held the edge. Generally speaking it enables me to glaze plates without any drip marks. Really appreciated with translucent glazes. 

Here are plate tongs made from plastic jar covers. (For some reason the image is sideways?) The many holes prevent the lids from holding glaze which then drips onto your still wet plate. The little notches in the lid rim aid in holding the plate edge. Once the glaze is dry I dab a little glaze where the lids held the edge. Generally speaking it enables me to glaze plates without any drip marks. Really appreciated with translucent glazes. 

Years ago, on another pottery blog, Clayart, someone mention that English potteries use "tongs" that are essentially strips of wire, extending from several fingers, that hold plates along the edge. The idea that holding the plate, along the edge, creates fewer noticable glaze tong marks, seemed like a good idea, to me. However, crafting wire in such a way that it could hold a plate firmly seemed challenging. So this is my alternative solution. 
My original thought was to use cookie cutters, thin strips of steel in other words, but I couldn't find cookie cutters that were big enough to hold a plate. Looking around my living space I saw a jar cover and thought it might work. Turns out these work really well. I need to grab the plate firmly, before I dip, but otherwise they hold 12" plates nicely.

Years ago, on another pottery blog, Clayart, someone mention that English potteries use "tongs" that are essentially strips of wire, extending from several fingers, that hold plates along the edge. The idea that holding the plate, along the edge, creates fewer noticable glaze tong marks, seemed like a good idea, to me. However, crafting wire in such a way that it could hold a plate firmly seemed challenging. So this is my alternative solution. 
My original thought was to use cookie cutters, thin strips of steel in other words, but I couldn't find cookie cutters that were big enough to hold a plate. Looking around my living space I saw a jar cover and thought it might work. Turns out these work really well. I need to grab the plate firmly, before I dip, but otherwise they hold 12" plates nicely.

And I understand that slow-cooling can add to the available effects from some glazes in electric kilns, by giving them more time to develop crystals.

Super Cool! Slow Cooling in an Electric Kiln
https://ceramicartsnetwork.org/daily/article/Super-Cool-Slow-Cooling-in-an-Electric-Kiln

From https://digitalfire.com/picture/bestenazoh

Firing for Atmospheric-like Effects in an Electric Kiln  https://tinyurl.com/cf7ef94y
Fuel-burning kilns tend to be much larger than electric kilns. Because of their size, they usually have a slower heat rise, a soak at the top temperature, and slower cooling cycles. If you want similar results from an electric kiln, especially when firing to cone 6, one of the most important things you can do is emulate the heating and the cooling cycles of larger kilns. This means slowing the temperature gain to about 100°F (38°F) an hour during the last several hours of the firing, soaking the kiln at the top temperature, and then down-firing to slow the cooling cycle.

Electric kilns are built with thinner insulation and legs (to allow for air circulation), and they cool very quickly, especially at higher temperatures. If you are seeking buttery, matte surfaces but have trouble achieving them in the electric kiln, it is most likely due to fast cooling. Matte surfaces are usually caused by microcrystal growth during cooling, and, if the cooling cycle is too steep, there isn’t enough time for crystals to develop. In extreme cases, I’ve even seen matte glazes go glossy and transparent.
... note that the 100F(38C) above is "finger trouble", see 
What is the difference between fahrenheit degrees and degrees fahrenheit? https://digitalfire.com/picture/2704

Glazes coloured with stains, not sure about that. Maybe these days, with lots of folk buying commercial glazes
My shelves still full of the mineral chemicals needed for the colours. Been firing midfire forever it seems. Amazing the effects using an electric kiln, though I pine for my gas one  still.
Electric kiln a good starting point if you're doing it by yourself.
Enjoy it all!