A few examples of these Chocolate dials can be found randomly among all the references with caliber 321 movements. On the other hand, we have noted a large number of reference 145.022-69 models with this particularity, mainly between movement numbers 29.110.xxx and 31.009.xxx. Most have a dark chocolate hue, which is more difficult to discern in poor light. There do not seem to be any Chocolate dials on references after 145.022-69.
In the 60s/70s, the brass blanks for the dials underwent a series of preparatory operations before being colored by electro-plating.
The anthracite-colored coating came from an electrolyte bath containing a nickel zinc alloy, called black nickel. Dials plated with such alloys needed an additional layer of protective nitro-cellulose varnish to prevent oxidation of the plating and the deterioration of its anthracite color.
However the nitro-cellulose varnish was porous and of varying quality. Humidity or long exposure to UV light could break it down and thus open the way for the oxidation of the plating with an alteration of its color.
The chocolate hue was thus the result of the nickel-plating oxidizing.
Later galvanic baths improved in quality and the nitro-cellulose varnish was replaced by a synthetic varnish that was much more resistant.
The significantly higher proportion of discolored dials in the reference 145.022-69 models could arise from a batch of dials with defective varnish. Their color might have changed without the agency of extreme climatic conditions. Note that the discoloration of the dials fitted to the 145.022-69 models is minor and not necessarily visible in insufficient light, thus the dark chocolate name.
The discoloration is not always regular over the entire dial, since the oxidation starts at the abrupt angles where the layer of varnish is at its thinnest, especially on the edges of the subdials.
The milk chocolate dials are the result of the oxidation process at a more advanced stage, due to harsh environmental conditions (humidity, sulfur compounds and UV radiation). Watches that have spent years in damp tropical climates or in sunny regions are likely to be more susceptible to this phenomenon.
Chocolate dials are particularly sought after by collectors today as a fine example of how a defect becomes a valued rarity over the years.
Thanks to Jean Singer & Cie SA for their technical explanations.
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3 responses
Thanks for educating us !
By logical deduction, I think there is a connection between the dial manufacturing process
of the famous 2.2-2.3m Rolex 1680 Red Submariner brown dial (Singer dial), and the 1969
Speedmaster Chocolate dials. My guess would be the processes and materials used would be
the same, causing the same result for a brief period of time.
You’re perfectly right, this is probably the right explanation. Such tropical dials have been seen on many watches equipped with Singer dials.