Roberta12

I did test tiles of black underglaze with  brighter colors of underglaze over the black.  I was pleasantly surprised to see the bright colors stayed bright.  I thought the black underglaze would "swallow" the  brighter colors.  It did not.  However, black porcelain is different that painting a test tile with black underglaze.  It really will be something you have to test.  I was using Amaco Velvets.  

As others have said, much of the glaze surface could be had by a speckled clay body. However, if I were experimenting, I would try using iron rust mixed into a White or off white glaze, you might even try adding some Rutile, powdered to a glaze white glaze as it has a tendency to make a more buttery looking color. . . then add the iron rust to that. When I say iron rust, I mean to scrape some rusted metal to get irregular sizes of iron, then grind it some to remove the larger particles screen it through a 200 to 300 mesh screen. Depending on the size of particles  you with to include in the glaze. Then comes the fun part, deciding how much iron speckling you want in the glaze. Lots of testing, but could be a great learning experience for some more advanced motivated students.
(For some reason or other, I got this on to another strand about a glaze search. . . Mod-Min brought my error to my attention)
 
best,
Pres

Good to know!  Of course it does depend on what kind of underglaze you are using.  I don't have Amaco Velvets though I keep meaning to get some to try.  I agree, doing tests - that's always wise before you commit to working on an important piece.

I did test tiles of black underglaze with  brighter colors of underglaze over the black.  I was pleasantly surprised to see the bright colors stayed bright.  I thought the black underglaze would "swallow" the  brighter colors.  It did not.  However, black porcelain is different that painting a test tile with black underglaze.  It really will be something you have to test.  I was using Amaco Velvets.  

I did test tiles of black underglaze with  brighter colors of underglaze over the black.  I was pleasantly surprised to see the bright colors stayed bright.  I thought the black underglaze would "swallow" the  brighter colors.  It did not.  However, black porcelain is different that painting a test tile with black underglaze.  It really will be something you have to test.  I was using Amaco Velvets.  

I don't unload the bisque (I fire at a community centre so the technicians load/unload) but do rinse after wet sanding and after that it's glove only handling until after they are glazed. I've had scrubbing damage the underglaze in the past so i only use a sponge now, but wet sand in one sink basin & rinse in the second basin. 

Looks like Axner has a good per pound price.
I'm not seeing that suppliers near me (Northern California) carry it ...Claypeople in Richmond has it.

I get it from my clay supply house.  I have seen it listed at different clay supplies online.  Check with your clay supplier.  

Is this a commercial brushing glaze, a commercial dipping glaze or a recipe you mixed yourself? How are you determining how thick to apply it? Is this a cone 4 glaze specifically, does your clay mature at cone 4? F it’s mixed from a recipe post it here.
Glaze crawling like you are experiencing has a few main reasons why it occurs. Contamination of pot surface by dust or lotion/oils on hands, glaze application too thick or raw glaze has excessive shrinkage. Reason it’s that yellowish colour where it has crawled into little islands is because it’s thicker there from the glaze crawling together. 

1. Consistent wall thickness, carve when leather hard, keep moist or covered until carving is done
2. Very narrow cutting blade , best ones are less than 1/8”, needle tool to fish out trimming scraps
3. Plan holes so that there is enough structure to hold itself up when high heat softens the clay at the peak of firing, geometric designs are most reliable 
4. Dry slowly, covered loosely 
5. Gently smooth rough edges with a green scrubber when clay is no longer damp
6. Some experimenting will be necessary to determine glaze thickness and application 
7. Clean excess glaze from holes with a needle tool
Here’s a video from a Korean master: 
 
 

Chances are the underglaze is too thick.
- What color underglaze is it happening to?
- When are you applying the underglaze? Leather hard, bone dry, bisque?
- How many coats, and are you thinning out the underglaze before applying?
- How are you applying the glaze?

I’m a big fan of Ravenscrag slip in recipes, but I can get it easily. It should be able to be special ordered in the US from anywhere you can get Alberta slip from. They’re from the same supplier. It gives a good white gloss over the red clay I use, but you want a satin. 
Currently I’m doing some testing on Sue’s Calcium Matte from Glazy, and trying to take it into satin territory. It’s got really great colour response, but I’m finding it crazes a bit, and the iron tests  discoloured with vinegar overnight. I’ve got a line blend with silica going into the kiln next week that I hope will address those 2 problems. I can share results in about a week and a half from this writing. 
 When creating a white over red clay, if you have a glaze that already has the flow and application characteristics you like, mix a batch without the usual colourants and add 7-10% total opacifier instead. I prefer to mix opacifiers, because it tends to make for a more interesting glaze. I like titanium and zircopax, or tin and zircopax, usually just a 50/50 split. If you do this, use at least a small cup for a test tile. Using the usual 2” extruded guys won’t give you enough of an idea of the subtleties that will show on your main body of work.
In choosing a base glaze, think about whether or not you want to completely obscure your red clay with the white glaze, or if you want some texture to show through. If you want some texture, a well melted or slightly fluid glaze will be better. If you want a more majolica look, look for something stiffer. 

@Roberta12 This mixing matte and gloss works great!! I have a base of G2934 at 40% and a clear, G1216M, at 60%. This base has given me white, tan, yellow, turquoise and gray liner glazes. The glazes are very durable. 

This one is my favorite on buff clay.  Or light brown clay.  I am still in the semi testing phase. 
Off White Semi Matte  (you can find it on Glazy.)
FF3134        28.0
Silica               16.0
Talc                    15.0
EPK                    14.0
Ravenscrag Slip     13.0
Ravenscrag Slip Roasted     13.0
 Zircopax            7.0
 

You have it right, the manufacture has it right, the inspector has it wrong. Interestingly a 60 amp breaker is the minimum allowed. Breakers that you buy for home are usually rated and thermally limited in load to no more than 80%. 80% of 60 amps is 48 amps. Lots of folks know the 80% rule so if it dawns on him he may suddenly change his mind. In the end your electrician has it right and can point him to the NEC and NFPA requirements for a continuous load - resistance heat. Basically not less than 125% nor greater than 150%.

There isn’t a difference in the tax amount on a $40 item with a $20 shipping fee and a $60 shipping included item going to the same place, the way RevCan calculates it. The $20 (closer to $25 in real life) in the equation is the pre-tax cost of shipping and ought to include a little padding for shipping materials and shipping cost variation. 
Since you’re adding this charge to whatever your mug retails for, there should already be some money incorporated into that base price that’s expected to go towards anything you have to do to sell the piece. If you’re not paying for booth fees, travel expenses and wrapping to use at a market,  that money gets put towards your web hosting and helps offset the odd overage in shipping. 

@grackle, for dark clays or those with a lot of impurities to burn out it's important to slow the bisque firing down between 1300F through to 1650F. It's in this temperature range inorganic carbons will burn out. Try slowing your bisque firing down 60 -100 degrees F per hour and see if that helps. For dark clays coloured with manganese try firing to only cone 5.
Another way to get a nice matte glaze and be able to adjust how matte you want it is to blend a gloss glaze (without colourants or opacifiers) with a quite matte glaze. If you do a simple line blend with the gloss and add increments of 10% of a matte glaze you can see how adding the matte will negate some of the gloss. If you want to try this a good recipe to use is this one. Once you have the level of mattness (if that's a word) you like then add zircopax (approx 10%) or tin (approx 5%). If you find the zircopax makes it too matte (because it adds silica also) then tweak the gloss slightly higher.

Thanks for the responses! I figure I will likely treat this first re-glaze effort purely as an experiment. Maybe try the underglaze on top, bisque fire (for better adherence?); then satin clear at cone 5. Will later repeat building the same form, but with the revised glaze choices I feel good about. Interesting term "eutectic" btw...have something to perhaps stump the glaze teacher with.

I have had about 50% success with reglazing and refiring.  If the place is on the interior of a bowl or cup, I simply put more glaze on it and fire away. That is very successful.  If it is on the exterior, I set the piece in front of a small heater or use a heat gun to warm the piece, then quickly put the glaze on.  For me it depends on the glaze and where I am trying to reglaze on the pot.   @Callie Beller Diesel had some excellent points about the underglaze.  But....as @Bill Kielb  said, you don't know until you try!
 

My skutt 10 cubic foot kiln -48 amps wired with copper #6 wire is hooked to a 60 amp breaker-the 125 rule is in effect and youir inspector is not familiar with that for kilns. You can educate them of do the 50 and swap out later if they are hardheaded .

Hi Frogesan,
Welcome to the Forum!
Kiln wiring comes up quite often here.
The experts (I'm not an expert...) point out the 125% rule, etc.; try using the built in search using "125%" to find a few, e.g.
https://community.ceramicartsdaily.org/topic/31343-skutt-822-wire-gauge-size-vs-breaker-size
As for burning down the garage, going with a too small breaker should just result in the breaker tripping, nuisance trips!
Running too small a wire with too large a breaker could get hot, I believe (I'm not an expert!).
For reasonable run lengths, #6 wire, correct? 
And for runs much over fifty feet, start looking at the next bigger wire?
Any road, the kiln manufacturer's documentation looks correct to me, and it lines up with what the more expert regulars on this Forum say.
The wiring for my new 48 amp kiln was recently completed, 60 amp breaker, per specification.
I only needed the two hots and a ground, however I ran the neutral (and left it capped off on both ends), just in case someone comes along years from now and needs/wants the 120v, having recently ran into a similar situation with our son's wellhouse (wiring for 240v well pump), where we wanted 120v to run some water treatment equipment...

Thanks, Roberta:  I would love to have the recipe.   I always test any new glaze on my various clay first.  I got several of the recipes I used in college (many years ago) from the pottery dept there, but for some reason, they no longer had the white.  The college used the same clay I am using now, so it seemed logical.  I read something about  those dark iron rich clays needing more oxygen in the bisque fire to burn off more carbon and prevent bloating.  I have a downdraft kiln  which supposedly has enough oxygen, but do not know how to introduce more except by leaving peepholes open?.

skutt and L&L are correct.  I ran into a similar situation when I got my kiln.  And  because the building it was going into was new construction and we had to upgrade our electrical,  and the inspector didn't have experience with kilns.....we ended up hardwiring my kiln at the inspector's command.   And we went with the 60 amp breaker.  I talked to Steven Lewecki at L&L and he was proper upset with our inspector, but....there it was.  The upside of hardwiring it was that my insurance company was very happy about the hardwiring. So I guess there is that.  Would hardwiring it make a difference to your inspector?
Roberta

Hi, I'm buying a new kiln and having my garage wiring updated for it. I haven't picked out which model yet, but all the ones I'm looking at have the same electrical requirements (kiln needs to be on 60-amp circuit).
My understanding is that because the kiln is a continuous load, one that draws 48 amps needs to be on a 60-amp circuit. My electrician agrees, although he's not a kiln expert.
I've run into problems with the inspector, who INSISTS that I must use a 50-amp breaker in the garage subpanel because the kiln has a 50-amp plug. The current (ha) plan is to put in the 50-amp breaker to pass inspection, then swap it out for a 60-amp breaker so I don't burn down the garage.
Just as a sanity check, can someone confirm that Skutt and L & L are right about what size breaker I need, and the inspector is wrong?
Thanks!

Thanks, guys--have been away from the computer.  I am looking for a satin white, that will work on either my Cinco Roja clay or my Cinco Blanco clay from Armadillo Clay in austin, TX.  I also work with the Nara Porcelain from Aardvark (I think).  All cone 6 clays, but to be honest, I fire to Cone 5 because I have determined my L and L kiln fires a bit hot., based on repeated cone results.  I like to use stains with the white glaze.