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   This weekend, a friend who is technical coordinator for the geology
department at a small University showed me a plaster relief model from
the late 19th century of the Four Corners area that he found in the
basement of the geology labs. It was evidently prepared for (or under the
auspices of) the USGS. (Back in those "halcyon" days when John Wesley
Powell was director...his name was on it).
   I'd like to find appropriate information on the proper way to restore
this to it's original state. Does anyone have any references for such
work?
  Thanks,