Kiln Coatings

There are a number of coatings available for application to the inside of the kiln, aiming to increase its thermal efficiency and/or protect the kiln wall or elements.

Emisshield

This aims to increase thermal efficiency by absorbing heat from the flue gases and re-radiating it over a much wider range of wavelengths, so it isn't just reabsorbed by the flue gases. So perhaps just works with gas kilns? See here for an article on it.

ITC Coatings

The one best known to potters, though their claimed results on this reseller site seem pretty unbelievable!
Claim to both protect the kiln and reduce heat loss.