Lesson #33: Reducing block warpage ...
(contributed by Dave Bull)
For printmakers using plywood 'blocks', warping isn't much of a problem, but for those of us using solid boards, avoiding warping is an ever-present consideration. No matter how well, and for how long, the wood has been dried, it still retains its ability to both pick up and release moisture from the air. The problem of course, is that wood absorbing moisture expands as it does so, and carefully carved blocks will be thrown out of registration.
The most difficult situation to deal with is a block that has absorbed (or released) more moisture from one face than the other, in the process becoming warped into a curved shape. (Lumber people have specific terms to describe different types of deformations: cup, wane, bow, warp, etc., but I am simply speaking in general terms ...)
Boards that have been improperly dried are probably going to warp no matter what you do with them, but there is one very important thing that you can do as a matter of general practice, to help avoid it: never leave a woodblock lying flat on one face for any extended period.
A block lying flat on your workbench is free to 'breathe' from only the top surface - whatever atmospheric changes are taking place will affect only that surface. Moisture may be flowing into the block, or out of it, but in either case the block is being 'stressed' as that exposed face tries to either expand or shrink. The inevitable result will be a warped piece of wood.
Every block that is not in use at the moment should be kept leaning up against the workshop wall, or should be stored away with both faces covered.
So when you're carving, and take a break for lunch, please slide your block off the bench and lean it up somewhere so that both faces are exposed to the air. You'll help avoid problems ...