The original finish on a prewar bike should be the equivalent of a similar period automobile. The finish should have a standard high gloss nature but not the overly glassy look achieved with some modern paint systems and clearcoats.
Here is the scoop on Colson Serial Numbers.
A friend of mine specializes in prewar Colsons and has a reasonably large collection of them. We logged the serial numbers of his bikes and the few I have. Comparing the serial numbers to the models, we noted patterns that generally worked to tie the individual bikes to the year they were produced.
Beginning with the 1937 models the serial numbers usually consist of two lines of information. One is a letter followed by a number and the other is four or five numbers.
The conclusion we drew from our sampling is that the number in the two character line represents the last digit of the year the bike was produced. The letter may represent the month of that year but our sampling to date is not large enough to confirm this.
The caution is that the sampling to date is large enough to show a pattern but not large enough to confirm the pattern and some Colsons are not stamped in a manner that fits this defined pattern and decoding.
On the bright side, the bike you are working on does fit the pattern, so, first of all I would guess that the 1 in the second line may be an “I “. The 8 in that line following our decoding would represent production during 1938. The four numbers above are likely a sequential code relative to the two character base code.
1937 codes appear to be reversed, with the two digit code above the four/five digit one. From 1938 most of the bikes have the larger code placed above the shorter one.
Typical codes by year would be:
F7 over 12345 equals 1937,
12345 over F8 equals 1938,
12345 over F9 equals 1939,
12345 over F0 equals 1940,
12345 over F1 equals 1941,
and 12345 over F2 equals 1942
The bikes we identified as pre 1937 have one line codes as opposed to two line codes and several of the 1934 and 1935 models have the last digit of the assumed year of production located at the front of the serial number.
Examples would be: 4 B1004 would signify 1934 and 5H2188 would signify 1935. The 1936 bikes we recorded did not follow either the earlier or later patterns.
No postwar Colsons were included in the sampling so I can’t speak to whether or not the prewar pattern holds true for postwar bikes.
I’ll end this with a reiteration of the caution that the numbers we were working with are a small sampling of Colson production. Anomalies and alternative interpretations of the Colson serial number system may surface as additional numbers are added to the model.