Good question. Can be frustrating, enough to make your eyes water sometimes !!! Difficult but doable. Where do we start ???
Clues !!! How is that for vague ??? But really how do you date anything old ?? Circumstantial evidence it seems. Even a whistle with the date stamped on it can be difficult at times. Now, if it is a military whistle then the date on it is actually pretty good right ?? AND if it is hallmarked it is very accurate. However for most of the field, it is Sherlock Holmes and powers of deduction….
Where do we start then ??? ….
Patents >>> depending on what the patent is for and for how long it was good for at that time of issue.
Registrations >>> when it was issued and how long good for.
Catalogs >>> unless they used an old picture, otherwise works well.
Advertisements >>> whatever date of ad.
Manufacturer >>> the dates he actually was in business.
Internal parts >>> major telling point !!!
Design >>> takes lots of experience looking at different whistles though.
Comparison >>> Easy to overlook this one !!! ( note the previous discussion on Tudor Rose rounds.)
Now take as an example…. You get your whistle and look at the stamp if any. Do you know the maker right away ?? That would help the production dates a lot. If not stamped by the maker then the perhaps the stamps the maker used for others ?? Listed in Collecting Police Whistles for many UK whistles.
Next, the all important parts inside — which many times were specific to that maker ( however sometimes several manufacturers used those parts or designs ) Now go on to design characteristics. Do you have similar ones to compare to ??
Is the word PATENT on it anywhere ?? >>> Even on the disc if tube shaped.
For what was the patent issued and to whom ??
We had several whistles in a row that looked alike, then one came with the manufacturers name on it. That told us who made the others and that helped to date them.
Really one is getting to CIRCA for the most part. Sometimes getting right down to the year if all falls into place, but usually not so. More like a period of time is doing really good. And keep in mind, it may take years to unravel. Or should I say to peel back clue by clue…
Like peeling an onion ??