Q. I just bought some lumber from a small mill and they were not certain but thought it was honey locust, but it might be elm. Any ideas how to separate the two?

A. Honey locust and black locust (unrelated species actually) both will fluoresce a bright yellow color when exposed to blacklight. Elm, hackberry, oak and most other common woods will not show any response.

We will see fluorescence in rare species like pawpaw, redbud, Kentucky coffeetree, sweetbay and sumac. You can get safe backlight bulbs at hardware stores.