Inspect a watch with a loupe 
before buying.

by Watchking

A loupe can help you to predict future flaws. I just finished appraising a group of watches for an estate trustee in New Jersey. He thought my inspections were "surgical". I used two different kinds of loupes. The point is that on a pre-owned watch there are various future problems that can be predicted although they can not be seen with the naked eye. In addition you can often find problems in a newer watch that a reputable company will fix because it was a latent manufacturing defect. To make the customer happy, reputable companies will take a watch back for inspection at any time. 

If under loupe inspection a few tiny grains of luminous material are found somewhere on the dial (usually the edge) it is a sign that the binder in the paint is giving up. If there are one or two tiny oil spots showing under the center posts for the hands then the dial finish will likely be shot in a year or two as oils migrate and lift dial paint. If there is a tiny bit of paint crackle in any area, then the watch was likely worn in the sun a lot and each exposure will cause more crackling of the finish. If the crystal glue is uneven or if there are tiny pits on a trim ring under a crystal it is quite possible that the crystal was smashed at some point due to a hard shock and unless the entire movement has been replaced, this watch could have many future problems. As well, fine glass-dust is one of the worst materials to get into a watch and can destroy a movement within a year of normal wear. 

Tiny wear-through of gold filling or plating that is NOT visible to the naked eye may be easily seen if a loupe is used. Chemical polishing that can clean off and protect from tarnish for a week or two cannot keep you from seeing the edge of the gold/brass line with a loupe. The brass areas will eventually tarnish and darken. After-market bezels, replacement dial pips, poor dial refinishing, dirty day and date wheels and oxidation on a watch's hands are all much more visible using a loupe. 

There are other areas to check with a loupe as well. Check the thread cleanliness on a screw-down crown and the threads on a screw on back. Look inside for the jeweler and cleaning marks. Watchmakers often wear loupes to put the date of a watch’s cleaning or repair inside on the caseback. You can’t see these marks without a loupe. Check the screw heads on the movement plates as well. If the heads are scratched or worn then the watch has likely needed major repairs. You might want a watchmaker to inspect a watch in such condition before you buy it. 

Many collectors are approaching their 40s or 50s now and they may have lazy eyes that can overlook a flaw that later becomes unpleasant when it has been pointed out to them. A loupe helps to avoid this problem. In addition it is often easier to see that a dial is off-center in a case or that one of the pips on a dial has begun to come loose if a loupe is used. A simple "Sherlock Holmes" or "square reading" magnifying glass will work just as well. Small problems not visible to the naked eye can easily become big problems later and often a seller is offering a watch at a very low price because the seller has seen a problem under a loupe and is hoping that you won't. Even new watches have problems. Of course on a new watch if you are not totally satisfied you should just return the watch. If the dealer isn't co-operative then not only return the watch but stop doing business with this retailer. 

Various kinds of magnifiers and loupes are useful for inspections. The 10x Hastings triplet is the classic color-free magnifier that jewelers prefer. They are small and require a bit of squinting to use. 2.5x-6x magnifiers worn on the head are nice because they leave your hands free, and some models are stereo so they can be used with both eyes open. Nikon makes an achromatic magnifying glass in various magnification amounts that is a personal favorite of mine because it is multicoated and thus non-reflective. At the other end of the spectrum is the uncoated plastic magnifier popularized by Agfa that is passable at 6-8x and only costs about $5. Even a simple magnifier can save its owner more than its cost on the first buying trip it is used. I would not recommend getting a loupe with more than 20x magnification.