Bad lamp films can cause serious damage
- 16 February 2015
Most Enigma machines were historically supplied with a rectangular green filter
that could be placed over the lamp panel in order to increase contrast
in broad daylight. When not in use, the filter is usually stored inside the
top lid of the wooden case, held in place by two metal clamps.
While restoring a number of historical Enigma machines,
Researchers at EnigmaMuseum.com
have now discovered that some of the original
acetate filters have a tendency to decompose into acetic acid, which may
lead to oxidation and deterioration of the keyboard, the surrounding metal
parts and potentially even the interior.
The image on the right shows Enigma machine with serial number 12430
of which the metal key tops have been corroded badly by acetic acid
from a bad lamp filter . The metal bracket that holds the spare light
bulbs was also affected .
In this particular case, the machine had been stored for several years
in a climate-controlled environment, which rules out any other possible cause
for the corrosion. Meanwhile, more cases of corrosion have surfaced,
which have triggered this urgent warning to existing Enigma owners.
It seems that the problems are caused only by a certain type
of lamp filters. These bad filters can generally be recognised
by their light-green colour, as shown in the images
on their website.
Based on the
research of Enigma historians like Dr. David Hamer, Frode Weierud and
Dr. Tom Perera, it seems likely that about 10% of the surviving Enigma
machines are affected.
If you know of any owners of a WWII Enigma machine, please help
them by passing them this message.
Please note that the alert page on the CryptoMuseum.com website,
is an evolving page that will be updated with new images and
solutions as and when they become available. So please check this
page regularly for new information.
→ More on the CryptoMuseum.com website
To show you just how serious the damage from these kind of filters can be,
consider the rightmost two images above. The rightmost one was taken 3 years
ago and shows the keyboard of an Enigma machine.
As you can see the key tops are still shiny and there are no traces of corrosion yet.
The second image from the right shows the machine
just three years later.
The following actions are recommended
- Identify the type of filter
The suspect filters have a light-green colour and are not very dense.
When stored in the top lid of the wooden case, you can easily see the
wood behind it. Only a minor part of the wartime Enigma machines
were supplied with this type of filter. These filters often show some
kind of 'fogging' on their surface.
- Check the machine for corrosion
Carefully check the keyboard - and especially the metal rings of the key tops -
for traces of corrosion. This corrosion will appear as green 'mold' or
green 'rust flakes'. Also check the metal bracket that holds the spare light
bulbs in the top corner of the lid of the wooded case and the two metal
retaining clips that hold the lamp filter in place.
The image below shows the suspect light-green filter at the centre.
It shows a large contrast with the original - proper - green filter at
the left. As you can see, the proper is much more dense. The filter at the
right is a reproduction filter that is available as a recommended alternative.
If either of the above is true
- Remove the green filter
If you have a light-green filter and/or corrosion around the key tops or
the spare lamp bracket in the top lid of the wooden case, remove the lamp
filter immediately and store it elsewhere, preferably in plastic bag.
- Ventilate the machine
Leave the Enigma machine open in a well-ventilated room for at least one
hour, to ensure that any residual gasses are dissipated.
- Report the serial number
Please e-mail the serial number of the affected Enigma machine
to us, or directly to
This might help
us to pin down the serial-number range of machines that were supplied
with this type of filter. 1
- Replace the green filter
You may want to consider replacing the lamp filter with a reproduction one.
Proper lamp filters with the correct spectral range and density can be ordered
from various places for approx. USD 250.
- Restore your Enigma machine
If only minor oxidation is found, it may be sufficient to clean the metal
parts. In that case, inspect the machine from time-to-time, to see if it has
deteriorated any further. If your Enigma machine has been seriously
damaged however, you should consider having it restored professionally.
In that case, please contact us for further information.
A database of serial numbers and photographs of Enigma machines that have
been affected by corrosion of this type, is currently under construction.
Please help us to expand our knowledge base, by supplying as much information
about your machine(s) as possible.
We will treat your information with the utmost
confidentiality and will respect your privacy. Photographs of your machine(s)
will only be reproduced here with your permission.
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© Crypto Museum. Last changed: Tuesday, 17 February 2015 - 08:01 CET.