fired clay -bonsai soil

Do you use the clay after the bisque firing or after the glaze firing bit don't use any glaze?

I'm not understanding your question. Are you considering somehow firing your own clay-based bonsai soil?

I don't have any clue how you would get the fired clay broken down into small enough particles.

Much easier, IMO, to buy a bag of Turface.

I'm in a ceramics class and I have some extra vases I don't need I was wondering if I could just crush them up and use them soil

Sure you could. But figure the amount of unwanted pot you'd have to crush to get enough "soil" to fill up even a small 5x7 shohin pot. And then determine how you'd crush the pots into reasonably consistent 1/8 - 1/4 inch pieces.

There likely are easier ways.

I would not. You really don't know what chemicals are in that clay or glaze. And, in my experience, when you try to break up ceramics as you are considering the particles are dangerously sharp.

As I stated I would not use a glaze and aren't the particles suppose to be sharp? Jim I've used a tamp to break up lava rock before.

This really isn't worth the trouble or effort to do. You will be planting in something that is more akin to glass, not turface or pumice. Bonsai pots are meant to be mostly impervious to water, or at least less porous than the soil particles they hold. Crushed bonsai pots are probably a poor alternative to turface or other stuff because the particles aren't are porous and won't hold as much water...

Bisque fired clay remains porous & would be a good addition to your potting mix but only if your scrapping the work.

As I live in a remote area in NY I have often found it necessary to improvise. Many years ago I took to making my own pots. I'd often noticed "red clay" soil mentioned in bonsai books, so when I did a bisque (1st) firing I'd add a bag of basic clay kitty litter and the results were very much the same as the Turface that I now use. If you attempt to use kitty litter check the list of ingredients on the bag. Two things to note: make sure there's only clay and do a test firing of a small batch before going ahead and firing the entire bag. The last bag that I fired came from Florida. Nothing against Florida but that was the only difference from my previous bags of kitty liter. A couple of hours into the firing, thick yellow smoke (sulphur dioxide) filled the room and was venting out of the building. I stayed nearby until the smoke stopped to make sure nobody got exposed to it. I felt bad about polluting the air but also very lucky that no one was injured. That was over 20+ yrs. ago.

If you're a ceramist throwing clay on the wheel, then this is an easy way to make use of scraps from trimming. Let it go bone dry, crush it (I use my hands), pass it through 2 or 3 grades of bonsai sifters from 1/8" up, and bisque fire it. Wash thoroughly to remove fine dust.

8 mm hand rolled ceramic balls.
Using the plant that likes the least amount of water,
our local willow leaf ficus [ Ficus p.]
Plus 1 part aged compost to 9 parts ceramic.
Laters,
Khaimraj

https://i.servimg.com/u/f20/19/00/27/56/ficus_12.jpg

https://i.servimg.com/u/f20/19/00/27/56/ficus_11.jpg