Hey Norm,

       That's a cool looking glaze!  5301 does some nice things.  I still haven't gotten around to making the aventurine with the Special RIO.  Maybe this weekend!

How hard is that going to be to take it up to ^6?  Would you be able to do that with the Iron Aventurine as well?  

I'm trying a ^6 without slow-cool tomorrow.

There are samples of the 100% 5301 and 20% Iron Oxide, with pancakes underneath, as well as the same with added Kaolin or Kaolin and Silica. I don't know enough not to try it.

The tile below is fired to ^06.  The Glaze is 100% Ferro Frit 3269, 20% Spanish Iron Oxide, with 16% Cryolite added to bring the Fluorine up to the 9% level found in the 5301 frit. With the Cryolite added I get Aventurine.

Clearly Fluorine is an important ingredient for a nice Aventurine glaze, likely as a flux but who knows what else it contributes?  I previously tried recipes without Fluorine, like the ones below the photo, which result in a more opaque Aventurine glaze which splatters in the kiln which is not anyone's idea of a good glaze.

Ugly Muddy Kiln Splatter Aventurines (too thick and they're matte brown)

What I meant was how much of what are you adding to the recipe before you take it up to ^6?  I could try some variations as well to see what we can come up with.  Jeff

Off the top of my head I added 10% EPK, which doesn't seem at all sensible now.

Upon reflection it seems I should add only 20% to 25% Silica to make it more refractory, with a Silica/Alumina ratio similar to other glossy high fire glazes.

I added 10% extra silica and 20% extra silica to my three low fire glazes. The 20% flowed just a little too much, the 10% extra silica flowed way too much, so I think adding 24% Silica would be perfect to make these low-fire glazes into ^6.

I now realize if I increase the glaze by 24% silica also I needed to increase the amount of oxide colorant by 24% as well. That seems pretty obvious in retrospect.

Using the same 10% nickel carbonate with 20% extra silica there was less green crystallization as there was less nickel to go around. The 3269 frit with 0.5% chrome oxide, which Laguna calls Tang Lime Crackle, has slightly fewer crackles with 20% silica, but is far better at staying where you put it unlike the test ring below which fused with the pancake.

The Aventurine glaze came out dark and sparkly on brown clay, looking nearly identical to the bisque temperature aventurine without the extra silica, and similar to the tile below with 3269 frit with 16% cryolite added.

But the combination of being 24% short on iron oxide the melt lost so much iron to the white clay that I ended up with an amber glass with no aventurine.

One constant theme seems to be I get better results with Spanish Iron Oxide which gives a lighter amber xolor yet fully aventurine, and good result with the red precipitate iron oxide which is darker. The Laguna red iron oxide gives a bad result as does the black iron oxide.

Unattractive "test tiles" as I'm down to using abandoned bisqued pieces.

Ferro Frit 5301 100%, 20% Iron Oxide,

^04 first row on white clay,

^6 second row with 20% extra silica on brown clay.

Second photo 10% and 20% added silica on white clay, clearly not enough iron left in the melt.

It's amazing to see how far the fluorine 5301 frit has migrated into unglazed areas, especially with only 10% added silica.

You'll notice none of these samples,  either bisque-fired or Cone 6 fires have the beautiful golden brown you achieve, even on white clay. The sparkles are there, but when not in the bright light the glazes are black, with the exception of the Spanish Iron Oxide fired to ^04.

The 3269 frit 100% with 16% crylolite and 20% Spanish Iron Oxide, fired to ^06, is so far the closest in color to yours.

The results are interesting given the different levels of iron in each type of iron oxide.

72.4% __ Iron Oxide - Black - Fe3O4
69.9% -- Red Iron Oxide Red - Fe2O3
61.5% __ Yellow Iron Oxide  - I haven't tried this yet.
60.8% __ Iron Oxide - Spanish

Tomorrow I'll unload a Spanish Iron 24% with 100% 3501 and 24.8% Spanish Iron, fired to ^6, but this time our usual firing schedule of 30 minute hold at the top followed by a 50F slow cool between 1,800F and 1,500F

I like the lighter color glaze melt the 60.8% iron content Spanish Oxide produces, adding less iron and extra silica.

Next best I like the high purity precipitate with 69.9% Iron.

Black Iron Oxide with the highest level of iron 72.4%, gives the least amount of  of sparkly crystals

According to the 2004 "Potter's Dictionary" the crystals are haematite, made of pure Fe2O3 red iron oxide. I notice some use up to 30% iron oxide.

http://books.google.com/books?id=TApnGTVLwxAC&pg=PA17&dq=wh...

This is the same ^06 glaze shown in this topic header: Ferro Frit 5301 with 10% Nickel Carbonate,

But with 20% Silica added - then fired to Cone 6 using our 50F/hour slow-cool between 1,800F and 1,500F.

One white clay on the left, and brown clay on the right.

xanthan gum? I use that in gluten-free flour!