The seasoning process is a normal part of plancha cooking. The initially silver-looking surface shows the outline of items placed on the plancha. It is not necessary or desirable to scrub off these marks.
The plancha reaches its final black state after it has been cooked on a few times; this is known as the seasoning process. The plancha does not look very appealing during this transitional phase and can even seem somewhat deterrent. The plancha is entirely black in its final state and completely non-stick, as you might have encountered with some old cast-iron or steel pots. The general rule is: the blacker, the better!
Once the surface is well seasoned you won't need any oil or fat for cooking a la plancha. You can help the seasoning by frying some potato skin with a good bit of oil. Don't forget to keep them moving on the surface. Rest assured, the result won't be edible but whatever you'll barbecue afterwards will taste the better.
How to clean your plancha
The duck breast is cooked on a new cast aluminium plancha. The first outlines of the seasoning process are already visible.