Was it a good coating?

An engineer makes the first visual inspection of a VLT primary mirror surface after the coating. Since telescopes spend the night under the stars, the mirrors accumulate on their surfaces a certain amount of dirt which reduces the reflectivity and degrades the image. For this reason, the VLT 8.2-metre primary mirrors (M1s) need to be cleaned periodically. The cleaning of the M1s is a very delicate operation which takes place every 18 months and involves removing the aluminium by chemical washing and then recoating the mirror.