Blue Dun (from the illustration in Favorite Flies and Their Histories - 1892 by Mary Orvis Marbury)

Hook: #14 dry
Thread: light dun (gray)
Tag: gold
Tail: three light dun bucktail hairs
Body: light blue dun (here flash dubbing)
Wings: light blue dun hackle tips
Hackle: light blue dun

Head cement recipe:
Goop
Xylene (epoxy thinnner)

Instructions:
Fill a quart jar half full with Xylene
Squeeze a tube of Goop into the Xylene
Shake until the Goop is dissolved; add Xylene to desired consistency

Apply with a pin or needle dipped in the liquid

https://youtu.be/AJbvJUixaCs