Clayboard or Claybord
Claybord is an archival and acid-free hardboard coated with acid-free porcelain made by Ampersand:
"Ampersand uses a two part emulsion process for sealing the hardboard before applying our different acid-free grounds. We first apply an acrylic sealer that seeps into the fibers of the hardboard and then we do a final sealing layer to create a barrier between the wood and the ground.
This barrier will ensure that over time the lignans in the hardbord will not interact with the grounds or your paints. Each of our grounds whether it be the acrylic gesso on Gessobord or our clay-coated grounds for Claybord smooth, Textured Claybord, and Pastelbord are non-yellowing and have been created to give the artist a variety of surface options to choose from. These grounds are carefully "poured on" to the surface and dried to ensure excellent adhesion with the sealing layer.
sealing process along with our acid-free coatings gives artists painting
on Ampersand’s wood panels the assurance that their work will be around
for a long time. We realize that in these short paragraphs we couldn’t
cover everything, so please give us (Ampersand) a call if you have any
further questions – (Or see webpage below) 1-800-822-1939."