Here are some damage definitions to watch for when buying or describing your mugs.  Not all types of damage are equally damning to the values.  A chipped mug, for example nearly kills the value entirely, and you’d only want one chipped if it is both rare and needed to start or complete a set.  A fleabite on the other hand decreases the value somewhat but not entirely.  Deep cracks are almost as serious as chips.  Other types of damage vary by degree and its impact on price will be up to the buyer and seller. click on any mug for a larger view.

Here is a small chip from the rim of a very rare mug.  A piece of glass about the size of a pencil lead is completely gone.  Chips are most common on rims then bases, then handles.

Here are two views of cracked mugs.  One from the outside and another from the inside since the fired-on color hides this green mug’s crack from the outside.  The rubber coated I have found to be extremely frail for some reason.

Color loss, flecks of paint missing, and worn off colors can vary widely in terms of seriousness.  Try to get full color, bright, shiny color finishes.

Maybe hard to see in this picture, fleabites are tiny chips.  These are approximately the size of a pinhead and can be seen only with close visual inspection or rubbing your fingers around the rim or other edge of a mug.  These should not be mistaken for rough edges from manufacturing though.  Fleabites can knock a mug down from mint to very good condition.  Unlike a chip or crack, a fleabite may not necessarily make the mug unsuitable for daily use.

This one is hard to see but looking toward the right side in the picture notice that the gloss is bright at the very bottom and top and less in the middle.  The glaze in the middle is missing.  It will look like someone took steel wool and scrubbed it heavily.  However, the missing glaze cannot be explained by washing, daily use, etc.  because of where the missing glaze is found.  Sometimes on these incomplete mugs, some of the color pattern was never applied at the factory.

Some mugs will be found with a crack at the handle where it meets the body of the mug.  It seems odd that one side will be cracked and yet the handle not completely separate from the mug.  Also, there will be found some cracks that are not deep, from manufacturing at the handle connect point.  The degree of damage will vary by how clean the cracked handle appears.

For the mugs that are coated with a gold or silver rim, as in the Happy Home mugs or this leaf mug, they should not be placed in a microwave oven.  The metal will spark and where the sparks fly the coating will be burned, discolored or removed.  These areas should be cleaned lightly to help retain their shine.

The rubber coated mugs will be susceptible to mold or mildew if left in moist, or uncontrolled environments.  They can be cleaned only on the outside.  Also, sunlight will fade the colors of the coating.  The formal name for these was "Glamalite", and came in a boxed set of 8.

Notice the crooked application of the decal.  Given a choice, choose the mugs that are the most flawless in all respects.  Other manufacturing problems include small wrinkles in the glass, tiny roughness at the mold seams, and incomplete glaze as noted above.

Possibly an increasing problem is fakery of mug decals.  Here is a nice application of a Royal Canadian Mounted Police, a sticker from the 50s applied by a homemaker to this standard footed mug.  Decals are easy to find and you’ll want to make sure that the decorated mugs you buy are factory authentic or authorized.

This little white mark on the inside of this mug is a sign of excess pressure or weakness in the glass at the time of mfg.  These white marks are actually weaknesses in the glass and extra care should be used in handling them because they can break or crack more easily than a solid and strong mug.

This old mug has simply seen a lot of good honest use and cleaning.  Showing surface scratching, loss of glossy finish.  The damage is consistent on the entire mug including the inside.