[old_tv_nut]

?? Reference ??

There are two kinds of shadow mask warping, neither of which produces a "wavy' pattern, but instead a color purity problem.
1) thermal warp from high beam current - can occur with a constant area of high brightness, but reverses when the beam current is lowered
2) mechanical warping from dropping the set - permanent

By wavy pattern, do you mean moire'? This is a design issue of dot size vs. scan line spacing, and is permanent for a particular tube design.