Mary,
The digestive enzymes of leps are fairly powerful acids, so obviously could disolve whatever it was after so it could retrieve it. Chemicals in the crete itself or residue from something left behind from any of many sources. Might have been from your feeders, bird droppings, a spill or runoff of some other composition it found worth the long visit. Gave you a long close up op which is always enjoyable
L.

Red admirals must have a unique need for chemicals or minerals or whatever, Mary. My road/driveway is gravel. I've been seeing a red admiral "nectaring" on the gritty ground there in the late evening ever since we moved here and had the road put down in 1996 - must be a VERY old butterfly! :0
Other butterflies stick their proboscis in wet soil, but they do this every evening, even when the road is dry. Maybe they're "spitting" in the grit when it's dry? :)
Some of the individuals have been very friendly, landing on my arm - another reason to think minerals have something to do with it, especially if my arm was sweaty/salty.
So I guess if you want to attract red admirals, you could plant false nettles AND make them a gravel garden. :/
Sherry

red admirals also like nectar flowers including zinnias, liatris spicata, and verbena bonariensis. They have been scarce this year because of our cold spring, but were frequent visitors last summer....just in case you don't want to create a gravel garden ;)

I have plenty of native and non native plants for nectar. The other numerous butterflies were all over the plants but this one hung out all day. I have been gone this morning but have not seen it today.

Miss Sherry - I read in one of my books that male Red Admirals "often take territorial perches on sun-spotted driveways and other locations in the late afternoon, reappearing for many days in a row at exactly the same time and place." Sounds like what you have experienced.

I do have false nettles but haven't seen evidence of eggs or cats on it.

Pretty butterfly! Haven't yet seen one here this year. Have my fruit out though.~~A

All leps that feed as adults need more than just the carbohydrates, amino and organic acids, proteins, ions, vitamins, oils, etc they get from flower nectar and pollen. Flowers are not created equal, why some species are more highly regarded by leps than others and some are completely ignored. So "puddling" on damp soil, decomposing plant or animal remains/byproducts, sweat, sap, honey dew, mineral "licks" and many other sources are used by various species to get what they need. They sometimes regurgitate their digestive enzymes to help the process along, sometimes do not need to. Some species are more prone to using these sources that others, some to using only them and mostly just ignoring flowers. In the tropics especially finding a source can be the key to finding some species. So baiting them is a common method used, especially for those species that carry out their entire lives in the canopy and seldom come down to the ground or those who seldom venture out of the deep, dark understory. Baiting works well in NA too for many species, but will be ignored by many others as well.
FWIW

I forgot to tell you how gorgeous your picture was, Mary, so I will now - it's gorgeous!

I think what you read is just what I've been experiencing all these years. I checked out the false nettles yesterday evening, and there aren't any caterpillar nests on them, so I do think this one is a male, just like all my previous driveway males. They're all fond of gravel "nectaring", then flying over the driveway in bouncing motions. I'll try and get a picture of a driveway male soon.

Sherry