Wood ash refractory formula?

Does anyone know how to make refractory material out of wood ash and maybe clay or other natural easy to gather resources?

You must have picked up my own vibe of coming up with my own recipe as I'm experimenting right now with the same thing.
My first brick was made with 1 part homemade charcoal, 1/4 part local clay soil and rock wool fibers. After drying it, I would say it is about as strong and delicate as the traditional perlite/clay risers.
My second attempt (still drying) is 1 part wood ash (with small bits of charcoal), 1/2 part local clay soil and 1/2 part horse poop. Seems to be not as fragile but we'll see once it dries.
I think Donkey at proboards has a few recipes but haven't gotten there yet to peek. He built the cyclone batch box with neolithic materials and in the video said he used crushed old firebrick, wood ash, clay soil and cow poop
Love to hear about others recipes also.

great ideas
i have no background in chemistry or masonry, but have heard rumors there was a way to make fire brick and such with hardwood ash

UPDATE: I wanted to keep the materials as simple and readily available as possible, therefore the clay and sand I used in the following recipes were both harvested from our property, not commercial products. After the brick was dry, I put it into my wood stove for several hours to bake on the hot coals to fire them and see how they held up. Shrinkage was maybe 1/8" on most bricks for length and about 1/16" for width. Here are my results so far.

Brick #1 (from my previous post): After firing the brick crumbled apart into powder with very little effort. The rock wool fibers were hard to keep separate. They kept wanting to clump up as I teased them into the mix and found the fibers to be really short and easily broken into smaller and smaller pieces. Because of this I would say they provide very little if any tensile strength to the brick which was my intention for putting them in. For this reason I'm going to leave this material out of my bricks.

Brick #2 (from my previous post) - Dried nice and firm. After firing though same as #1, it crumbled apart.

Brick #3 - 1/4 part broken bits of commercial firebrick splits, 1/4 part horse manure, 1/2 part clay slip, 1/2 part wood ash.
Held its shape really well before and after drying but after firing, it crumbled apart.

Brick #4 - 3/4 part wood ash, 1/2 part sand, 3/4 part clay slip, 1/4 part horse manure
With the sand it turned out much heavier once dried. After firing, the sand turned orange and when lightly rubbed was chalky. Stronger than the first 3 but still broke easily. Weight 3lbs

Brick #5 - 1 part wood ash, 1/2 part clay slip, 1/2 part rock wool (one last chance), 1 heaping tbsp furnace cement mixed with water
Held together quite well even after firing. When rubbed its somewhat chalky (from the wood ash). Little bit of crumbling at edges but in all would say the furnace cement made all the difference.
Rock wool was in clumps and if at edges would sometimes fall off. Dull thud with finger flick. A little heavier than some of the others About 3.5lbs
EDIT: After handling it more, it did crumble apart as well.

Brick #6 - 1 part wood ash, 1/2 part clay slip, 1 part perlite, 1 heaping tbsp furnace cement mixed with water
Similar to brick 5 but when you flick your finger on the brick it makes a ring sound similar to pottery. Weighs about 3lbs. The brick is 9x4.5x2 3/4"

Brick #7 - 1 .5 parts perlite, 1/2 part clay slip, 1 heaping tbsp furnace cement mixed with water
Lucky 7! This is the best one yet for being light & strong. Rings when flicked and looks similar to a commercial insulated brick to me. This is similar to Matt Walkers cast core recipe just in different proportions. Havn't tried it with fiberglass matte (as he did) to see if it helps with strength even more.

Brick #8 - Same formula as #7 but with twice as much furnace cement...still drying on the stove before I fire them.
EDIT 2 - After firing it may have a bit more of a ring to it but seems just as strong as 7. Will need to put it through some sort of abrasion test to know for sure.

Hi, just passing through.

What's the thinking behind horse manure as a refractory material? Charcoal has good heat insulation but would need regular replacement as it's eaten away by the fire. The charcoal would also need to be a fine powder to mix with the rest of the aggregate.

Iron oxide (rust) is an additional improvised material that might work. You can also make improvised lime from (roasted) shells of garden snails.

With cement (store bought, wood ash, snail shell lime etc) the bricks would need to go through multiple wet/dry cycles to cure. Say, 10 days maybe? After that, the bricks would need to be dried out in an oven/fire at a moderate heat to drive out any remaining moisture before subjecting them to the full torture of a furnace. Improvised refractory is possible, but you'd need to do a lot of work either searching how they did it long ago or through a lot of trial and error.