I did a lot of research and decided to buy tempered hardboard instead of untempered to make painting panels. The processing of tempered hardboard used to have an oil in it that made it unsuitable for artists to paint on. But painters are now using it because it's now manufactured with a process that gives a perfect support with no oil residue and a much stronger board. It's not prone to warping as easily as standard hardboard and it is a much harder and denser material. Leading art supply companies are recommending it as well and are selling it as their panels.
I bought a 4x8' sheet and got 10 painting panels of various sizes from it:
• two 24x36" (61x91cm) and two 20x24" (50x61cm)
• one each of 24x28", 18x24", 16x24", 14x18", 10x10", 8x10" (61x71cm, 45x61cm, 40x61cm, 35x45cm, 25x25cm)
I had the board cut twice at the lumber yard so I could get it on the back seat of my car (two 36" wide cuts and what's left is a piece 24" wide). At home, I cut my pieces out with a circular saw, sanded them, and wiped them all down with paint thinner. There was no oil residue at all on the rag.
My next step will be to seal the panels with a coat of oil-based polyurethane or acrylic matt medium on all sides. I will cradle the bigger ones first before coating with a layer of polyurethane. After this coat has dried for a couple of days, I will sand and apply acrylic gesso in the regular way.
