Min

Agree with you that gum(s) are great for hardening powdery raw glazes and with some glazes that just don't want to layer up without lifting. I'ld hazard a guess there is much more gum in a commercial brushing glaze than what would be in a dipping glaze to prevent those issues though.

This came up the other day, might help. https://community.ceramicartsdaily.org/topic/41668-midfire-clay-short-when-recycled/  Given your reclaim is already on plaster slabs if it is still fairly wet I'ld put it back into a bucket with some more water and add the blunged bentonite or ball clay/bentonite and slurry mix it again with the plasticizers. The smaller the clay particles the greater plasticity you will get from them, bentonite is much finer than ball clay which in turn is much finer than EPK. 

I agree that stacks of test tiles can get fiddly and overwhelming but tests are so useful! I’ve made simple reference pots for my stain tests using bisque, straight-sided mugs, cups or bowls of the preferred clay, one for each base glaze, and as many small deli cups as you have stains to test.
Dip the pot almost halfway into the glaze and let dry.
Mix 1/8 tsp of stain into 1T of base glaze in each carefully marked deli cup and stir up, add a little water to make it brushable, if needed.
Paint 1/2” wide vertical stripes of each color from top to bottom, over the dipped glaze and over the bare clay.
Dip the bare end of the pot almost halfway into the base glaze, covering the stripes, and let dry. There will be a space between dips to show you what the stain in a bit of base looks like on bare clay - handy for white clays.
After the firing, use a sharpie to label the stain stripes with the stain numbers. Make notes if you want to try different proportions in a future test.
I use these little deli cups to decorate from, mixing more as needed (stains are expensive!) and letting them dry up between uses, adding water by drops to rehydrate.
NOTE: be sure you make note on the pot of which end is Glaze Over and which is Glaze Under. It won’t always be obvious  
 
 

I wouldn’t use either of those glazes if you are new to glaze chemistry as it would be necessary to remove some of the other fluxes in order to add zinc. If you just added zinc then the glaze would have more flux than needed to create a balanced glaze. Result would be an excessively fluid glaze.
Glazes high in magnesium tend to have a more muted response to colourants than those without high levels of it and blues  from cobalt lean more towards purple tones.
Yes, zircopax will give more of an opaque glaze, with or without stains. Starting at around 5% addition will show, 10% will be opaque on most bodies. 
A green stain that contains chrome when put in a glaze containing zinc will most often give an unpleasant brown.
Your second link didn’t work for me.
Welcome to the forum.

Pinched your fingers yet? (yup, I've done that a few times )

For future searching, please note this should read Giffin Grip.  No "r", "i" not "e".   

Pinched your fingers yet? (yup, I've done that a few times )

I question the testing using the same piece for each subsequent heat increment as each cycle will stress/shock the glaze. I know that's the point but I agree with Hansen's take on this. I sometimes go 300F/ice water, then 315F/ice water then 325F/ice water. If a glaze doesn't stress craze from this I don't think it will with everyday normal (sane) usage. 450F to ice water IMHO is far too extreme! We are after all making ceramics, not metal bakeware. It does seem logical to soak the test piece for 12 hours after a reasonable stress/shock testing though.
edit: In the past I did try the boiling water / ice water testing, had a glaze that passed it so went ahead and glazed a load of pots with it which later went on to craze. I'm sticking with the oven/ice water test, greater difference in temp therefore a harsher test, either the one above or just 3 sets of samples at 315F. 

Pinched your fingers yet? (yup, I've done that a few times )

I question the testing using the same piece for each subsequent heat increment as each cycle will stress/shock the glaze. I know that's the point but I agree with Hansen's take on this. I sometimes go 300F/ice water, then 315F/ice water then 325F/ice water. If a glaze doesn't stress craze from this I don't think it will with everyday normal (sane) usage. 450F to ice water IMHO is far too extreme! We are after all making ceramics, not metal bakeware. It does seem logical to soak the test piece for 12 hours after a reasonable stress/shock testing though.
edit: In the past I did try the boiling water / ice water testing, had a glaze that passed it so went ahead and glazed a load of pots with it which later went on to craze. I'm sticking with the oven/ice water test, greater difference in temp therefore a harsher test, either the one above or just 3 sets of samples at 315F. 

Pinched your fingers yet? (yup, I've done that a few times )

My guess would be it's because of different reflected indexes between the glazed and unglazed surfaces while in the microwave. 

Hi and welcome!
Stains are fun to work with, especially for us dark clay users. And the reference chart you’ve already found is a very good reference is this section of Digitalfire. Tony identifies the stain by number, which is a good practice as there are 3 different numbered stains with the name “dark red” and they all have slightly different chemistry.Tony’s got examples of the Canary Yellow and Turquoise in a magnesium matte glaze base, so you can see how those 2 respond, at least.
Speaking of recipes: the second  link you’ve shared comes back as a “does not exist” error. If this is a recipe on your own page, make sure it’s published so we can see it. 
Zircopax won’t make the colours pastel: glaze colour theory doesn’t work the same as paint. If anything, it’ll make it brighter and more saturated, because more of the colour is reflected back to your eyes. 
 

Maybe you mean ASTM 554? It calls for three passes of going from 250F to room temperature water without crazing. Repeat at +25F increments up to 450F. Crazing fails the test. Too much work for me!  I just rely on three passes of boiling water to ice water to determine whether it's going to craze or not. It is a little bit more of a cheat for me because boiling water at my altitude is only 199F. Although the microwave test calls for doing ASTM 554 first, to me, the two tests seem mostly independent.  If you are going to determine whether a piece is microwave safe, microwaving it and seeing if it gets too hot seems to be enough for me.

It is coincidence that @davidh4976 mentioned a clay body so high in iron that a magnet will stick to it and I received in the mail today the strongest magnets I’ve ever seen. So, of course I had to play.. My clay is a local iron rich earthenware that vitrifies at cone 03. Not all the pots do this, apparently only the ones that are reduced heavily and fired to maturity. 

I question the testing using the same piece for each subsequent heat increment as each cycle will stress/shock the glaze. I know that's the point but I agree with Hansen's take on this. I sometimes go 300F/ice water, then 315F/ice water then 325F/ice water. If a glaze doesn't stress craze from this I don't think it will with everyday normal (sane) usage. 450F to ice water IMHO is far too extreme! We are after all making ceramics, not metal bakeware. It does seem logical to soak the test piece for 12 hours after a reasonable stress/shock testing though.
edit: In the past I did try the boiling water / ice water testing, had a glaze that passed it so went ahead and glazed a load of pots with it which later went on to craze. I'm sticking with the oven/ice water test, greater difference in temp therefore a harsher test, either the one above or just 3 sets of samples at 315F. 

I wouldn’t use either of those glazes if you are new to glaze chemistry as it would be necessary to remove some of the other fluxes in order to add zinc. If you just added zinc then the glaze would have more flux than needed to create a balanced glaze. Result would be an excessively fluid glaze.
Glazes high in magnesium tend to have a more muted response to colourants than those without high levels of it and blues  from cobalt lean more towards purple tones.
Yes, zircopax will give more of an opaque glaze, with or without stains. Starting at around 5% addition will show, 10% will be opaque on most bodies. 
A green stain that contains chrome when put in a glaze containing zinc will most often give an unpleasant brown.
Your second link didn’t work for me.
Welcome to the forum.

Without going into too specific details to follow the ASTM... for cups and mugs put a cup of cool water in the corner of a microwave then with the empty test sample mug run it for 2 minutes at full power.  Handle temp must not exceed 60C/140F and  any of the other surfaces 121C/250F. Before commencing test the test pieces must be submerged in room temp water for 12 hours and also pass the ASTM 325F oven to water test. (which I don't have) Slightly different times and temps for plates etc.

Without going into too specific details to follow the ASTM... for cups and mugs put a cup of cool water in the corner of a microwave then with the empty test sample mug run it for 2 minutes at full power.  Handle temp must not exceed 60C/140F and  any of the other surfaces 121C/250F. Before commencing test the test pieces must be submerged in room temp water for 12 hours and also pass the ASTM 325F oven to water test. (which I don't have) Slightly different times and temps for plates etc.

Without going into too specific details to follow the ASTM... for cups and mugs put a cup of cool water in the corner of a microwave then with the empty test sample mug run it for 2 minutes at full power.  Handle temp must not exceed 60C/140F and  any of the other surfaces 121C/250F. Before commencing test the test pieces must be submerged in room temp water for 12 hours and also pass the ASTM 325F oven to water test. (which I don't have) Slightly different times and temps for plates etc.

You can for sure use wadding in an electric kiln to raise pots off a shelf or level shelves but I wouldn't use it on a glazed surface.
If you stack plates with wadding between unglazed areas on the plates chances are the plates will warp and deform at mid or highfire.
I don't know the price of setters compared to kiln shelves where you are but another option is to purchase small round kiln shelves and use those with short posts for setters. If you try this be careful to  line up posts to prevent cracking a kiln shelf when you stack them, make sure the posts line up.
 
When wadding is used in an atmospheric firing such as wood, salt or soda the vapours from the gasses in the kiln flash the pots but the areas where wadding is will resist the flashing.

Neoprene disc stuck to the wheelhead with a little water for the vast majority of my pots, no clay wads. For bowls and platters wider than the wheelhead I use a  large batt that I glued high density upholstery foam to and put that on a damp Xiem BatMate knockoff. Never felt the need for a Giffin Grip.

In a nutshell to pass the ASTM for "Microwave Safe for Reheating" there is mention of "no metallic surfaces" but no threshold limit  for porosity or absorption of the claybody. Ware must show no degradation after the test nor exceed specific temperatures after a set amount of time at full power.
I would hazard a guess that those discoloured areas on the plate have let moisture into the body which resulted in the plate getting hot when your son removed it from the microwave. Agree with you, that is one well fitting glaze to stand up for catering use then your home use for 20 years.

In a nutshell to pass the ASTM for "Microwave Safe for Reheating" there is mention of "no metallic surfaces" but no threshold limit  for porosity or absorption of the claybody. Ware must show no degradation after the test nor exceed specific temperatures after a set amount of time at full power.
I would hazard a guess that those discoloured areas on the plate have let moisture into the body which resulted in the plate getting hot when your son removed it from the microwave. Agree with you, that is one well fitting glaze to stand up for catering use then your home use for 20 years.

In a nutshell to pass the ASTM for "Microwave Safe for Reheating" there is mention of "no metallic surfaces" but no threshold limit  for porosity or absorption of the claybody. Ware must show no degradation after the test nor exceed specific temperatures after a set amount of time at full power.
I would hazard a guess that those discoloured areas on the plate have let moisture into the body which resulted in the plate getting hot when your son removed it from the microwave. Agree with you, that is one well fitting glaze to stand up for catering use then your home use for 20 years.