Glass is very tricky to photograph, even under the best of conditions. In the photo at top are two boiling flasks. The flask on the left appears to have a seam in the neck. It is not a seam; it is a reflection of the jointed translucent top, but it could be mistaken for a manufacturing flaw. This visual flaw was removed without compromising the rest of the natural reflections in the quartz glass neck. A tiny dimple was removed in the bottom as well.
In the photo below, the same thing occurred with two jointed boiling flasks in this group image. These appear on the right half of the before image. The dimples were not removed as they were not as prominent in the group photo.
Retouching is not about how much we can do, but rather, how little we can get away with. However, sometimes a tiny flaw can become an undesirable eye magnet, and then it has to go.