Borax is only slightly soluble and can be a powerful flux. However, it is hard to physically process due to its solubility. It clumps and hardens when wetted. If you have a ball mill, you might be able to wet grind glazes containing borax.
May enhance carbon trapping if dissolved as it has a lower melting point (740C) than soda ash (850C). Not much dissolves though (3g/100ml).
Lithium Carbonate
May be useful as additional flux or to alter the glaze texture
Soluble sodium source. Some will be needed to cause flashing and carbon trap effects.
Large amounts (10-20%) will leave a layer of salts on the surface of the glaze which becomes very glassy during firing and may carbon trap in reduction
Clays
Too much plastic clay in a shino glaze will cause crawling as the glaze shrinks during drying. To prevent crawling, partially calcine the clay content.
Kaolin
As kaolins are chemically very similar, they should easily substitute for each other
A line blend with just kaolin and feldspar should produce good results. 100% feldspar is somewhat glossy. 25% feldspar and 75% kaolin is a stoneware slip.
Stoneware Clays
Stoneware clays may have iron speckles, which will be visible in the glaze.
Stoneware clays are less refractory than kaolins and will require less feldspar
Iron clays
Redart
Used in Malcom Davis' shinos to develop red color on zero-iron porcelains
Yellow Ochre
Used by Japanese potters for underglaze decoration
FF 3269 has boron and alkali metal oxides and almost no other fluxes. Should preserve red flashing while also melting very aggressively.
This frit is hard to come by especially in large amounts.
Feldspar melt test
I tested multiple feldspar and feldspar-like materials by mixing them with water and applying them like a glaze. There were no additives like bentonite; I just used very little water (around 50g water for every 100g feldspar).
With the exception of Cornwall Stone, every feldspar on this list looked almost identical after firing. They were semi-glossy and milky white to gray. None were red where thin - the only red flashing came from where the glaze was almost wiped off of the tile.
The clay near the edges of the glaze did flash orange. This means that the reds and oranges in shino glazes must be happening in the glaze, not the clay-glaze interface.
Feldspar plus clay
Japanese potters claim that they are using recipes that are 95+% feldspar, but they are nowhere near as glossy as the pure feldspar tests. I think that their feldspar sources are highly contaminated with kaolin and silica, and are more similar to Cornwall Stone. At cone 6, Cornwall is dry and umelted, but may be more shino-like in week long firings.
To get the similar surface in a (relatively) cold and short cone 6 firing, I can add clay to the feldspar. This will also improve suspension and encourage crawling where thick. Since I want the glaze to be uniformly melted, I choose Nepheline Syenite instead of the other feldspars, which I have seen only partially melted at cone 6.
In my first tests, I made 80-20 and 70-30 nepheline syenite to EP Kaolin mixes. 30% EPK was too dry but 20% was too glossy and transparent. Perhaps 25% EPK to 75% Nepheline Syenite is a good ratio.
Next, I tried a 25% clay to 75% clay ratio with various clays. The kaolins were rather dry at 25%, but Kentucky OM4 Ball Clay and Goldart were both rather glossy. The ball clay glazes were also slightly yellow.
Grolleg Kaolin is the least refractory of the kaolins
Tile 6 Kaolin melts less than EP Kaolin
It's hard to directly compare how well Helmer Kaolin as it contains larger particles that are filtered out when sieving the glaze. Therefore the exact amount of Helmer kaolin added is inexact
Ball clays like Kentucky OM4 Ball Clay melt significantly more than kaolins. Since many Kentucky / Tennessee / Georgia ball clays are physically and chemically similar, I expect to see similar results with all southern US ball clays.
Depending on the firing and location in the kiln, 25% kaolin seems to vary quite a bit in terms of melt. The glaze is very sensitive to the heatwork in the kiln. I don't want to have a sensitive glaze, so I'll use a mix of kaolin and ball clay to smooth out the transition.
A glaze of 20% EP Kaolin, 5% ball clay, and 75% nepheline syenite should produce a pleasant surface while also staying relatively white.
It should also be possible to add other white-burning refractories like
I made tests containing 7% Redart and 15%, 20%, and 25% EPK. The rest is neph sye. Similar to the tests without redart, 15% kaolin was glossier and yellower, and 25% kaolin was too dry but very red. I think the Redart content is also a little high to produce softer orange colors. I chose 7% because that's the percentage Malcom Davis uses in his shino glazes.
A glaze of 22% EPK, 3% Redart, and 75% neph sye should be a good flashing recipe.
The red flashing recipe should be applied thin and watery. When poured over the rough bisque surface it should pinhole. Then the white shino, when applied over top while still wet, keeps the pinholes and textures.