Not all wooden tables are equally vulnerable, and knowing what is on yours changes how much care it needs. The finish, not the timber, determines what happens when a wet glass sits on it.
The Finish Is the Surface
Almost no furniture presents bare wood. What a glass touches is a coating, and coatings vary enormously in how they handle moisture and heat.
A hardwood table with a fragile finish marks more easily than a softwood one with a tough coating. The timber underneath is largely irrelevant to this particular question.
Matching Protection to Finish
A fragile finish argues for absorbent coasters that remove the water entirely rather than a barrier that holds a puddle above it. Sets built on that principle, of the kind at thirsty-stone.net, suit shellac and oiled surfaces particularly.
They also argue for a placemat under anything hot, and for wiping spills immediately rather than at the end of the evening.
The Common Finishes
- Polyurethane and modern lacquer: reasonably water and heat resistant
- Shellac and French polish: beautiful and vulnerable to water, heat and alcohol
- Oil finishes such as Danish and tung: penetrate rather than coat, and mark readily
- Wax: soft, easily marked, and easily repaired
- Conversion varnish and catalysed finishes: the toughest, common on commercial tables
Shellac Is the Fragile One
Common on antiques and reproduction furniture. It is dissolved by alcohol, marked by water and softened by heat.
A spilled drink on shellac can leave a mark within minutes, and a hot mug can soften it. Anyone with a French-polished table should treat coasters as compulsory rather than optional.
Oil Finishes Mark and Recover
Oiled tables absorb rather than resist, so water marks appear readily. The compensation is that they are also the easiest to repair: reapplying oil frequently blends a mark away entirely.
They need periodic re-oiling regardless, which many owners neglect until a mark prompts it.
Even Tough Finishes Are Not Immune
Polyurethane resists water for a long time and not indefinitely. A glass left overnight, repeatedly, in the same spot will eventually produce a mark.
Heat is harder on it than water. A hot dish placed directly on a finished table can produce a white bloom that is considerably more stubborn than a cold-glass ring.
Working Out What You Have
A small test in a hidden area. Denatured alcohol on a cotton bud softens shellac and does little to polyurethane. Water beading strongly suggests a film finish; soaking in suggests oil.
For anything valuable, ask rather than test.
Sunlight and Heat
Both age finishes. Ultraviolet light yellows and embrittles coatings, and dry heat from a radiator opens joints in the timber.
A table positioned out of direct sun and away from a radiator ages considerably more slowly, which matters more over a decade than any individual water ring.
Maintenance
Dusting with a slightly damp cloth, occasional appropriate polish or wax, and no silicone sprays, which complicate any future refinishing.