Product Knowledge and Adhesive Chemistry
This domain tests whether you understand why an adhesive behaves the way it does, so you can diagnose cure problems instead of guessing. Expect questions on cyanoacrylate chemistry, monomer types, viscosity, cure speed, environmental control, shelf life and remover compatibility.
How cyanoacrylate cures
Lash adhesive is a cyanoacrylate monomer stabilised with a weak acid. Moisture in the air neutralises the stabiliser and triggers anionic polymerisation, so ambient humidity is the catalyst, not a drying process. High humidity accelerates cure and can cause shock curing with white bloom; low humidity slows cure and reduces retention. Manufacturers generally specify 40 to 70 percent relative humidity and roughly 20 to 24 degrees Celsius.
Monomers, viscosity and speed
Ethyl cyanoacrylate cures fastest and most rigidly with the strongest fumes. Butyl cures more slowly and stays flexible with less odour. Octyl is the most flexible and gentle, with the slowest cure. Formulations also contain PMMA or rubber for flexibility, carbon black for pigment, fumed silica to thicken, and hydroquinone-type stabilisers. Viscosity ranges from thin, which wicks quickly along the bond, to thick, which sits on the surface and cures more slowly. Cure speeds are commonly labelled fast (0.5 to 1 second), medium (1 to 2 seconds) and slow (2 to 3 seconds).
Storage and shelf life
Store upright, tightly capped, in a cool dark place. Unopened adhesive lasts roughly 12 months; once opened, expect 4 to 8 weeks of reliable performance. Do not refrigerate an opened bottle, because condensation introduces moisture and shock-cures the product.
Worked example
In August, a technician reports the adhesive grabbing instantly, leaving white bloom and poor retention. Reasoning: at 75 percent humidity the monomer polymerises before the lash is seated. The fix is environmental first, with dehumidification and air conditioning to bring humidity into range, then a slower-curing adhesive and faster placement. Changing brands alone does not solve a humidity problem.
Traps that cost marks
Believing "medical grade" is a regulated standard rather than marketing language; mixing brands of adhesive and nozzle; storing opened adhesive in the fridge; assuming thicker adhesive means stronger hold; blaming the adhesive when poor isolation is the real cause of weak retention.