Alberta Slip is a close physical & chemical substitute for mined-out Albany Slip. It is blended by Plainsman Clays of Medicine Hat. Owing to its relatively high plasticity, recipes calling for more than 40% should introduce the excess amount by calcining it (along with any other clay in the recipe) to prevent excessive shrinkage which can lead to crawling.
For a lot more information on Alberta Slip go to digitalfire.com