Min

Looks like a cream breaking brown glaze. Sometimes called cream breaking rust or red or more recently there is a glaze called Folk Art Guild White that is the same type of glaze. High level of tin with a small amount of iron, application is crucial to get the breaking colour.

If the first glaze saturates a thin wall then you apply a second coat or glaze the clay can't absorb the extra moisture without pulling away from the clay. I'ld try adding some gum to the ash glaze and then apply the Leach glaze when the ash one is just dry enough to handle. Don't wait too long before applying the Leach glaze.
BTW the David Leach II glaze looks like a cone 10 recipe that someone has added just a titch of boron frit to. Does't look like a cone 6 recipe.

Soy wax works great on the bottom of pots, also smells less than paraffin wax when burning off.

There is a thread link below about Liquid Quartz with another link within that thread with more discussion on it.
https://community.ceramicartsdaily.org/topic/30248-liquid-quartz/
What was the definition for archival from Amaco? Seems odd that they market their velvets for use with or without a covering glaze but could not say the velvet finish was archival. 
 
 
 

Oh gosh, sorry, don't know how I missed that. Okay, so plan B would be to make up a slip and use some oxides to make a black. Slip needs to go on greenware, as soft leatherhard as possible to avoid fit issues. Also test the covering glaze over it before committing a "real" pot. There are recipes for black slips that contain various amount of colouring oxides, most include iron + manganese + cobalt and sometimes chrome also. Something along the lines of this recipe from Vince Pitelka. 

It’s not for food. Liquitex matte medium, a room temperature finish, may fit the bill. It’s UV protectant. Produces a satin finish. Reliable and long lasting. Your fired pieces should be archival without that though.
 

Hi Paula and welcome to the forum.
Glaze blisters are one of the harder things to figure out the cause of and remedy. Blisters can be from the glaze application, materials, the firing, the claybody, the application or a combination of these. Given when you refired to a cone lower it healed most of the blisters is a good sign. Do you use cones to verify your firing and confirmed you aren't overfiring? Have you tried an unfired piece  at a cone lower or only a previously fired piece? This is where I would start trying to solve this. Since we don't have the recipe(s) for the problem glazes we can't offer suggestions for altering those but the claybody, firing and application method could be areas to look at.
In this months CM there is a really good article on glaze blisters by Jeff Zamek, it is behind a paywall but you can access 3 free articles a month. It's well worth a read. Link to it here.
 

Oh gosh, sorry, don't know how I missed that. Okay, so plan B would be to make up a slip and use some oxides to make a black. Slip needs to go on greenware, as soft leatherhard as possible to avoid fit issues. Also test the covering glaze over it before committing a "real" pot. There are recipes for black slips that contain various amount of colouring oxides, most include iron + manganese + cobalt and sometimes chrome also. Something along the lines of this recipe from Vince Pitelka. 

I had a look through Hamer's Pottery Dictionary of Materials and Techniques and under the Crazing topic. Snippet from there reads "Where a glaze is overfired and then crazes it is because the overfiring affected the body more than the glaze." also "The crystalline silica in the body becomes fused silica and in this form it has a much lower rate of contraction. The glaze still has the same rate of contraction and therefore in proportion it contracts more when overfired than when correctly fired."
Hamer doesn't quantify how much overfired. I haven't seen it with a single cone higher firing, maybe more prevalent with very tight firing range claybodies?  

Hi and welcome to the forum.
Have you tried black underglaze? It can go on greenware or bisque. 

Oh gosh, sorry, don't know how I missed that. Okay, so plan B would be to make up a slip and use some oxides to make a black. Slip needs to go on greenware, as soft leatherhard as possible to avoid fit issues. Also test the covering glaze over it before committing a "real" pot. There are recipes for black slips that contain various amount of colouring oxides, most include iron + manganese + cobalt and sometimes chrome also. Something along the lines of this recipe from Vince Pitelka. 

@davidh4976, good job on subbing the Custer out. I like how much silica and alumina are in the formula, will make for a good durable glaze. I could see a bit of iron in the recipe if you ever wanted to tone down the blue a little.

After a bit of testing, I found a Cone 6 recipe that gives a good, deep blue color that stays blue even over edges/texture. I avoided Gerstley Borate, Neph Sy, and Talc.  GB because of end-of-production. Neph Sy because it somewhat contributes to hard panning. Talc because of recent quality. This has been tested and found to be craze free (boiling water/ice water test) on the following clay bodies from our local supplier, New Mexico Clay: Marilyn's BOD, Ochre, E-Speckled, Cashmere, and Chocolate (these are all of the Cone 6 clay bodies that we now support in our pottery).  On Chocolate, the glaze surface does not look as smooth as on the other four which look great. Here are the two recipe versions, one using Mahavir Feldspar and the other using G-200 Feldspar (because we have both in our supply!).
AMT      MATERIALS

27.6      MAHAVIR POTASH FELDSPAR

26.5      SILICA 325

15.3      FERRO FRIT 3134

18.4      EPK

12.2      DOLOMITE

   2.0      COBALT CARBONATE

102.0   TOTAL


 

 
AMT      MATERIALS

29.3      G-200 FELDSPAR

26.2      SILICA 325

13.9      FERRO FRIT 3134

16.4      EPK

12.2      DOLOMITE

   2.0      COBALT CARBONATE

100.0   TOTAL

I had a look through Hamer's Pottery Dictionary of Materials and Techniques and under the Crazing topic. Snippet from there reads "Where a glaze is overfired and then crazes it is because the overfiring affected the body more than the glaze." also "The crystalline silica in the body becomes fused silica and in this form it has a much lower rate of contraction. The glaze still has the same rate of contraction and therefore in proportion it contracts more when overfired than when correctly fired."
Hamer doesn't quantify how much overfired. I haven't seen it with a single cone higher firing, maybe more prevalent with very tight firing range claybodies?  

Yes.
If you want a more extreme test then go from a 300F oven to ice water. Boiling to ice water has a temperature difference of approx 180F whereas oven to ice water is approx 268F  difference. 
I used to do a sequence of 300F/ice water then 310F/ice water then 315F/ice water but I think that once you have done 1 cycle of oven/ice water you have stressed the glaze to a point where further cycles aren't valid.

Yes it can over time. If you have 3134 then you could reformulate the formula with that which would give you room for more epk in the recipe. Or add a small amount of epsom salts solution to help flocculate it. (after measuring specific gravity)

Years ago I moved from a soft water area (Liverpool) to a hard water area (Essex), and my skin stopped wrinkling when I had a long baths.  (Also I needed to use more soap, as hard water reduces its effectiveness.)
A suggestion that the effects of moving  from hard water to soft may be self-correcting over time.
https://kidshealth.org/en/kids/wrinkly-fingers.html
I suppose you might try experimenting with:
- pre-exposure skin/barrier creams
- slightly hardening the water you use for throwing (slightly because it may effect the clay)
https://sciencing.com/make-hard-water-8191733.html
https://www.usgs.gov/special-topics/water-science-school/science/hardness-water
General guidelines for classification of waters are: 0 to 60 mg/L (milligrams per liter) as calcium carbonate is classified as soft; 61 to 120 mg/L as moderately hard; 121 to 180 mg/L as hard; and more than 180 mg/L as very hard.

Atlanta refs to confirm your suspicions about water hardness.
https://www.atlantisplumbing.com/articles/city-water-vs-well-water/
City Water Vs. Well Water
2. Generally speaking, well water is hard water so a water softener is recommended for homes that use well water.
https://www.hydroflow-usa.com/georgia-water-hardness
Georgia water is considered soft water. The average water hardness for the Georgia resident is around 60 PPM. Atlanta, the most populous Georgia city has a water hardness level of 21 PPM which according to USGS water hardness measures is very soft.
PS In this context mg/L = mg/kg = PPM

I like throwing that clay but it made my skin itchy. Have you found this? 
I like how nice and tight it is, have some mugs and bowls made from it, parts unglazed and no staining after many years of everyday use, slip made from same body without sand brushed on unglazed areas.

I like throwing that clay but it made my skin itchy. Have you found this? 
I like how nice and tight it is, have some mugs and bowls made from it, parts unglazed and no staining after many years of everyday use, slip made from same body without sand brushed on unglazed areas.

Somewhat south of your location in Strongsville, OH, between Peninsula and Streetsboro, our surface clay goes down 80 to100 feet, and is I believe part of the Hiram Till deposit from the last glacial retreat.  It looks to be same as what you have in your yard.
I have been using this successfully for several years, mostly wood-fired to cone 10, but read on...
Un-amended, and fired in oxidation to bisque temperature it gives an attractive orange terracotta and a deep brick red at cone 6, which is probably its sweet spot.
Like most 'found' secondary clays it has a rather narrow window for vitrification but works quite nicely wood-fired to cone 10 in a 'neutral' (i.e. alternating oxidation and mild reduction) when blended with 25% fireclay (Hawthorne Bond) to provide additional alumina.  Color is an attractive (to me) dark red/brown with a purple tinge, and it gives nice effects with ash.
In heavy reduction at cone 10 it needs considerbly more fireclay to keep it 'open' and avoid bloating, that is, to counteract the fluxing effect of the high iron content in reduction.
I dig it wet, dry it, slake it and blend to the consistency of half-and-half, strain through window screen to remove large stuff, sediment briefly , then allow to settle in buckets for several months followed by air drying to throwing consistency.  This retains all the fine silt and the finer fraction of sand which moderates the shrinkage.  It throws nicely with and wthout the fireclay addition (blended as slip), much like a grogged body.
It gives a nice range of colors in ash glaze, depending on firing conditions,  but has rather high shrinkage which could be reduced by calcining a fraction, which I have not done since I have other simpler options.

Sewing, crocheting, jewelry making (with pieces I have made from clay) swimming, and I am teaching myself Tarot cards right now.  Always something.
 

"Climate Change" : Goldfinch,  budding lilac tree, & post-snow/freezing rain iced branches 1/24/24, in NH. I do some photography.  

Hobbies can keep your mind and body active.   Growing gourds is preparing for my next hobby,  one of these years my MS will prevent me from working with clay.  Gourds can be the shape of pots and are light weight.   You can varnish,  paint, dremel, stain and cut designs out,   I already have 3 big lawn bags filled with a nice variety of dried gourds.   I have started a small collection of gourd art for inspiration,  two of them are from Peru and one is from a gift shop on 5th avenue.   Denice

Creative activities?  Oh, there's a list.
Gardening is my outdoor creation, placing leaves and colours together to combine and contrast.  The challenge of getting seeds to germinate, cuttings to strike, flowers to flower, veg to eat.
Sewing, mainly household stuff like curtains, but lots of dressmaking too.
Fibre stuff - spinning, dyeing, weaving, knitting and crochet, mainly with sheep wool, but also silk, flax and alpaca. 
Glass - fusing and copper foiling and leading.

I use 4 main glaze colours for dipping glazes, all made from one base plus a clear liner, these are in 5 or 6 gallon buckets plus an accent glaze that is just a small container of glaze. When I used to spray glazes I had more glazes but could mix up smaller amounts of them since I didn't have to have a big bucket to dip them in. I find that using less colours makes a more cohesive looking display, I don't try and please everyone by offering every colour under the sun.