This is M340 stoneware glaze fired to cone 6 using the C6DHSC schedule. The L3954B engobe fires deep black (it has 10% Mason 6600 black stain). The engobe was applied by pouring and dipping at leather hard stage (inside and partway down the outside). After insight-live.com/glossary/8">bisque firing the piece was glazed inside using the base GA6-B Alberta Slip amber base. The outside glaze is Alberta Slip Rutile Blue GA6-C (you are seeing it on the bare buff body near the bottoms and over the black clay surface on the uppers).
Pages that reference this post in the Digitalfire Reference Library:
L3954B - Cone 6 Engobe (for M340), GR6-M - Ravenscrag Cone 6 Floating Blue, G2826R - Floating Blue Cone 5-6 Original Glaze Recipe, FLB - Floating Blue
This post is one of thousands found in the Digitalfire Reference Database. Most are part of a timeline maintained by Tony Hansen. You can search that timeline on the home page of digitalfire.com.