Pre-anodisation process:
i) Form a thin [5-8µm], unsealed anodic film on the clean surface of the aluminium components.
ii) It is preferable for the film to be 18soft 19 and may be produced at temperatures up to 30°C. The aluminium must be clean prior to the anodising process and, afterwards, must be satisfactorily rinsed to remove the sulphuric acid.

Что означает 18soft 19? Заранее спасибо.