A factory-coated plate arrives presensitised, so the workshop starts at exposure. The coating was applied under controlled conditions on a machine, which removes the most variable step in the process from a room where temperature, humidity and operator technique all differ from day to day.

The cost is shelf life and stock discipline. A coated plate is a dated item, has to be stored away from light and heat, and is worth less the longer it sits. For a workshop with irregular work or a long inbound shipping route, that is a real constraint.

Uncoated polished plate reverses both. There is nothing to expire and nothing to store carefully, but the workshop owns the coating step and the consistency that comes with it, which means owning the equipment and the technique.

The usual pattern is that high-volume, deadline-driven work buys coated, and workshops with an established resist they trust, or with sporadic production, buy uncoated. Both are legitimate; what causes trouble is switching between them without adjusting exposure.