Bisque firing in a Raku kiln?
Major difference between a raku kiln and a common electrical kiln is the heating capacity of the raku kiln being much higher. Raku firing is a fast firing technique where the kiln is fired to 1000 0C normally within an hour. A temperature controlled electrical kiln can be programmed such that the firing during the first couple of hours goes very gradually with a temperature rise limited to 60 or 100 0C per hour or so. A raku kiln, even with minimum gas pressure, is already quickly above 200 0C which is a dangerous temperature for work that is not completely dry (steam explosions).
To control and restrain the temperature rise in a raku kiln you can remove the lit from the kiln or put it half on the kiln and or vary with the burner being on or off until you work is completely dry. It is a matter of handling and firing the kiln actively. However to achieve a slow rising temperature curve like a temperature controlled electric kiln remains very difficult.
To compensate this you probably need to adapt the choice of the clay that you will be using. For example clay with more chamotte and/or larger grain size than it would be necessary if you would fire in a temperature controlled kiln.
In addition recognizing the moment where you can allow higher temperatures in the kiln because your work is completely dry is something that need experience.
Best way is to hold a glass or mirror above the flue gas opening in the lit. If there is moisture in the outlet air than this will condensate on the colder glass. When you do this it is important that the burner is being shut off. Otherwise you will always see condensate on the glass due to the burning of propane gas.
So you need to shut off the burner, wait some time to allow the last moistures flue gasses to exit the kiln and then check with a glass above the flue gas opening. When the work in the kiln is completely dry you will se no further condensate on the glass shortly after the burner is shut off. Is your work not yet completely dry, then the air will maintain to be moistures and condensate will appear on the glass even after the burner is shut off.
Conclusion:
Bisque firing in a raku kiln is in a certain extent possible however:
It may require concessions with regard to your choice of clay that you are using.
It require practice and building up some experience. A process that can include also a situation that you had the temperature too high too quick with work not being completely dry.
In practice this most likely means damaged work.
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