I guess that over the years I (ab)used this 1¼-inch-thick kitchen table top, by, for example, not using place-mats. The finish was initially extremely good. I palm-of-hand applied the varnish (which one, I can't remember). The idea was to use palm heat to push the varnish deeper into the grains. It worked quite nicely. But cleaning with a moist paper towel year-after-year ends up slowly sanding the varnish off.
Second mistake: I didn't apply the varnish on the bottom side of the table with as much vigor as the top side. As you see from the picture below, the bottom of the table was in any case not finished at the factory with nearly as much attention as the top side. (I understand that this is not unusual.)
Now aside from the irregular discoloration from food oils infusing into the top of the table, the more serious problem is that the top has warped. In the picture below, you see that it no longer sits flat on the legs and beams on the two short sides. The long sides are fine. They still sit perfectly flush with their beams.
In the next view you see the table top against the floor. Assuming the floor itself is still planar, the warping is quite serious.
Can this table top be salvaged? How?
I'm considering borrowing one idea from another (1⅛-inch thick) table top. On a desk table top that I have recently finished, I see that the manufacturer (a different one) has built a metal beam within a groove in the bottom of the table. They may have done this merely to give extra strength to the desk, since the frame carrying the table top does not quite reach the edges, rather than to stop warping.
My hunch is that if I now retrofit the kitchen table top with two metal L-beams, just next to the existing wood beams on the short sides, and force the table top straight by a number of screws through the two metal beams, then that would just be a recipe for developing cracks along the top the table, effectively ruining it. Do you agree? Both tables are of comparable dimensions: roughly 5ft x 2½ft.