white/gray rings on desktop

I have a black wooden administrators’ desk which develops a band (white or gray) matching the bottom of the cup or glass whether or not the liquid is hot or cold. The ring appears as a horrible circular stain on the varnished wooden surface and will not wipe off. But 5 or 10 minutes later the stain disappears. What causes this?

Yes, I’m aware that a coaster would prevent this. Still curious, however.

The condensation from the cup or glass collects on the desk, which causes the varnish to soften and turn opaque wherever the moisture is. The ring disappears because the varnish dries. You can actually scrape the varnish off with a fingernail when it is soft like that. Of course, I don’t recommend it, or you will truly ruin the finish.

Atropos: Thanks for your rapid response. Very apropos.

What do you mean “wooden” desktop? Whenever I have problems with my desktop I just reboot Windows…

smacks Grok with a big smelly Koi
Why in the world would you ever admit to using Windows?

You’re welcome MadSam.