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Stamp collectors from the 1930s might know this instrument. Today, researching this old "Macon Detector" is a challenge.

It's still sealed shut with clear cellophane, although the outer box was opened long ago. Here is most of what we've learned:

The instrument is from the mid-1930s (or earlier), and was designed to help collectors discern watermarks on postage stamps. This "watermark detector" apparently consists of the black plastic bottom "cup" section, and the glass top, with 3 round windows tinted blue, red and green. Printed in red letters on gold foil is this:

The Macon Detector
N.Y. City
Patent Applied For

Using benzene or another fluid in the cup, the collector would examine the wetted stamp through the colored glass. There is no battery, no built-in light source, no moving parts.

Diameter: 3" (7.5 cm)
Height: 1" (2.5 cm)
Weight in box: 3 oz

The brown cardboard box is about 3" square and 1" tall (8 cm by 2.5 cm). The gold paper label reads "MACON DETECTOR", with each word printed on its own banner. The center logo looks like a typical watermark, with a crown, cross, and 2 backwards C's.

The box manufacturer is still in business, since 1891. Their info is on one side of the lid:

No. P51
Mailmaster - Pat 1660279 [number indicates 1928]
The Mason Box Company
Attleboro Falls Mass

Apparently the similarity between "Macon" and "Mason" is coincidental.

In our quick web research, we did find a few more bits of info on Macon Detectors, including a link to a photo of the typewritten instruction sheet. It gives Glen Rock, N.J. as the company address. We will pass along the few facts we've found to the buyer of this listing. Listing consists of the "Detector", with the 2 halves still factory-sealed, and the box.

The box is beat up but intact. The detector has been handled a lot in its 70 years, but doesn't appear scratched.

Stored in a non-smoking home. A cat lives here. Thanks for looking, and Shop Etsy!

To the person who cut&pasted my description into your own Macon Detector listing on another site: you're welcome. I am glad you liked my words and even my punctuation.

Macon Detector for Watermarks 1930s Stamp Collector Gadget Original Box Unopened


  • Vintage item from the 1930s
  • Materials: glass, plastic, cardboard
  • Only ships within United States.
  • Feedback: 705 reviews
  • Favorited by: 5 people