Reddit reviews Primitive Technology II: Ancestral Skill - From the Society of Primitive Technology: Ancestral Skills - From the Society of Primitive Technology

Well one cheap way would be an earthenware and sand chamber with charcoal and a bellows... This is very labor intensive though and you might have an easier time building a small 'box' out of fire brick and run a propane burner into it. Such a structure built into the ground is very well insulated and maintains more consistent heat.You can probably do option #2 for 30 bucks or so...

If you want to go reeeally cheap you can always pit fire them... This involves an ordinary fire pit... slowly dry out the clay on the stones of the fire ring, turning regularly. Then move the pieces closer and closer until they are in the fire. Build a big fire around the pieces and let it burn all night. The slow heating and cooling cycle will temper it and the proximity to the fuel source will give the piece a lovely patina.

One note on using ancient methods- you can make almost anything using ancient furnaces and kilns that you can make with modern ones- you just have to make more of them because your results wont be as consistent and you are much more likely to break or ruin the piece. Size is also a consideration. Try not to get too attached to ceramics you intend to pit fire.

here's a couple of great reference books with great illustrations and directions...
http://www.amazon.com/Primitive-Technology-Book-Earth-Skills/dp/0879059117

http://www.amazon.com/gp/product/B00268EV9K/ref=pd_lpo_k2_dp_sr_3?pf_rd_p=486539851&pf_rd_s=lpo-top-stripe-1&pf_rd_t=201&pf_rd_i=0879059117&pf_rd_m=ATVPDKIKX0DER&pf_rd_r=1NQEHPV654RVB6RSZE4X