A series is rarely made in one sitting. It is made across weeks, between other work, and its enemy is not the model but the gap: the maker returns after ten days and describes the character from a memory that has quietly edited her. The ribbon exists for the gap. The card under it is read cold, exactly as written, and the new sitting starts from the record rather than from recollection.
Two habits make the return clean. First, the day’s line from the last sitting is kept with the card — outfit, corner, light — so the new line is written as a deliberate change from a known one, not a fresh guess. Second, the first frame of a returning sitting is judged twice as hard, because it sets the sitting’s eye; a drifted first frame forgives itself all afternoon.
Kept frames from earlier sittings are never used as the reference instead of the card. A frame can drift; the card, kept under its ribbon, is the only reference that cannot.
Series are not held together by talent or by memory. They are held by a marker, left in the right place, by a desk that writes things down.