I am having a circuit installed for my 27 amp kiln.

If you install the recommended 10 gauge copper wire that is required for your 27 amp kiln, you will not be able to power your larger kiln on that circuit later on. Since you think you may need a larger kiln later, wire the circuit with 6 gauge copper wire even though you now need only 10 gauge. (Six gauge wire is thicker than 10 gauge; therefore, the 6 gauge wire can handle a higher level of amperage than the 10 gauge.)