Authentication · 5 min read
Block acetate vs injection-moulded: how to tell in ten seconds
Two frames can look identical online and cost forty times different to make. Here is what to check on the temple, the hinge and the edge.
Almost every frame described as "acetate" online is one of three things: block-cut cellulose acetate, sheet acetate, or injection-moulded plastic that is not acetate at all. They wear completely differently.
Look at the cut edge
On block-cut acetate, colour and pattern run through the full depth of the material. Look at the inside edge of the rim, where the lens sits, and check that the tortoise pattern continues there. On moulded plastic, the pattern is a printed film or a surface spray, so the inner edge is a flat single colour.
Look at the hinge
Quality acetate frames have metal hinges pressed into a heated pocket in the material, usually with three or five visible pins on the front of the temple. Moulded frames commonly have a barrel hinge formed in the plastic itself, or a metal plate that sits on the surface with a visible seam line around it.
Look for a mould seam
Run a fingernail around the inside of the bridge. Injection moulding leaves a faint parting line where the two halves of the tool met. Cut acetate cannot have one, because it was milled from a solid slab.
None of this makes moulded frames dishonest — they are lighter and cheaper and there is a place for them. It only matters when you are being asked to pay acetate prices for moulded construction.