Emerald Gnat fly pattern from Favorite Flies and Their Histories (1892) by Mary Orvis Marbury

Hook: #14 sprout straight eye
Thread: black
Tag: gold tinsel
Tail: brown hackle barbs
Body: emerald green floss
Hackle: soft brown rooster
Wings: gray mallard quill

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