Picture series drift the way doorways seem to — never while you are looking at them. A frame is made in one week, another a month later, and by the third month the woman in the first frame is a stranger to the woman in the latest one. The cause is rarely the rendering; it is the measuring. She was paced out from memory at every job, and memory moves the frame a little each time it is asked. A card measured once and pasted every time does not move.
Five lines that never move
Age and build. One number, one build, stated plainly. Hair. Colour, length and the way it is worn. Face. Skin tone, features and expression. Signature. One small repeatable detail. Wardrobe register. The fabrics and cuts the series lives in. Everything else — the hour, the lamp, the side of the room — belongs to the line for this sitting, beneath the card.
The habit that holds a series together
Paste the card, work the sitting, judge the result against the card, and file the scores with the set. It is unglamorous work, and it is the entire difference between a set that reads as one woman and a folder that reads as a crowd.