While granite may indeed be the best enlarger table base, I only mention it in jest. I'd make an enlarger base out of it if I happenened upon a slab. Or if I was remodeling and had to buy the whole piece and was wondering what to do with the rest - rather than let the granite company keep it... Then by all means make an enlarger base out of granite. But the other materials mentioned are much, much more practical.
Another option is particle board that is varnished after the table has been completed. It's tough and dense, and with a few coats of polyurethane, it's rather attractive. I suggest using waterborne polyurethane floor finish form maximum toughness - and faster drying. Don't forget to sand between applications. Use a band of some kind of molding to cover the edges. It comes in 3/4" thickness and can be doubled (glued) if you want something thicker, but my experience is that if you have a support frame that extends around the entire outside edge, you don't need additional thickness to have something that is very rigid.
MDF is also a good material, but it's a bit softer than particle board. Glueing two 3/4" sheets together to make a 1 1/2" thickness should produce something that is reasonably rigid. MDF takes paint very well, but it's fundamentally thick cardboard, so it doesn't look that appealing when it is varnished.
At this point I've cut the mdf and am considering making it into a vacuum/steel table combo by adding a 1/2" layer of mdf around the edges between the top/bottom and a galvanized steel sheet on top with the holes all the way through the steel and top mdf layer. Best of both worlds.
I do have formica experience but would rather do steel, I think.
Sounds nice and very sturdy-----good luck with it.
Nice table there Chuck. I made one very similar but not as long.
If steel is used, it should be painted; shiny galvanized metal would probably reflect light back onto the paper.
I'd stay away from MDF having seen how it bows on bookshelves and such. Normal plywood would seem better. I'd probably do a sheet of plywood, a layer of honeycomb, then steel or formica. The honeycomb (as used in boatbuilding or other fiberglass work) would pass the vacuum and would add greatly to the dimensional stability without any weight.
I like granite too, but it would be impractical.
I gave this spare piece of 4x4 foot melamine covered 3/4" particle board to Jeff Bannow a few years ago to make a new table for his 10x10 DeVere Enlarger. I'm not sure if that project ever got completed or if it worked out ok or not.
1. I wouldn't use something shiny w/o painting it.
2. If I were to use melamine, it'd be the black stuff. The original was something melamine like but it sat in a vacant lab (broken windows, leaky roof) for many years before I bought it so the conditions weren't good.
3. the table isn't hard fastened to the enlarger so plywood (which warps because it has grain) is out.
4. I will coat all exposed surfaces with paint or polyurethane.