Every colour that leaves this workshop starts as a sprayed card, not a swatch printed in a book. The deck grows by a few cards a week and now runs to several thousand, filed by manufacturer and variant, and it is the first thing we reach for when a car arrives with a colour the instrument reads three ways. A card sprayed with our guns, our pressure and our clear tells us more about how a mix will actually land than any library formula, because it has been through the same booth the car is about to go into.

Hold a torch at a low angle to almost any car more than a year old and you will see fine circular scratching in the clearcoat — swirl marks, put there by car washes, dry cloths and grit. They are what makes a dark car look flat. Two-stage machine correction removes the clear immediately above them, which is why it can only be done a finite number of times and why we gauge the paint first: a car that has been aggressively polished twice already may not have the material left to survive a third. When it does, the difference is the single most dramatic thing we can do to a car in a day.

The gaps between panels are where a repair confesses. A door gap that runs from four millimetres at the top to six at the bottom tells you the car has been hit and put back approximately, no matter how good the paint is. We set gaps before paint rather than after, because a panel adjusted once it is finished is a panel with a chipped edge. On restoration work the gaps are set, taken apart, painted and set again, which is a fortnight of the schedule that produces no photograph anyone finds interesting and is the first thing an expert eye checks.

Every body shop website has them and they prove remarkably little. A dramatic "before" is a matter of choosing the angle and the light; a flawless "after" is a matter of a wet panel and a wide lens. Neither shows the two things that decide whether a repair lasts — what was done to the metal, and how many microns of what went on top of it. We photograph every car we work on, weekly, and those images go to the owner rather than onto a gallery page, because they are a record of somebody else’s property rather than an advertisement for us. What we are willing to publish is the vocabulary above: the deck, the swirl and the shut line, which are the three things anybody can learn to judge for themselves on any car, including one we have never touched.

If you are documenting damage for a claim, take more than you think you need, and take it before anything moves: the whole car from four corners, the damage from three distances, the opposite side for comparison, and the number plate of anything else involved. Shoot in daylight and avoid direct sun, which flattens dents into invisibility. If you are sending photographs to us for an estimate, a short video walking around the car in even light is worth more than twenty stills — it lets us watch how a reflection travels across a panel, which is how a trained eye finds a crease that a still photograph hides completely.