If you are looking for some data on a patent or want to estimate the date of a tool and it has a patent number there are a few things that might be of help. I am not an expert at searching patents so there is a lot I will miss but all are welcome to add anything.
First is Datamp - Directory of American Tools and Machinery Patents.
http://www.datamp.org/ If you have a patent number or a patent date this is probably the best place to start a search. It is not complete so the search may turn up empty here. This is a volunteer project so everything was done as a service to the community and no doubt they'd appreciate any new info you turn up.
Patents are granted on Tuesdays so if you think you have a patent date check the date if it's not a Tuesday it's almost certainly not a patent date but if it is a Tuesday it might be a patent date but not a guarantee it is.
It is possible to do a regular search engine on a patent number or date and I have gotten some good results.
Patent terms vary depending on year and modern patents are distinguished between utility patents and design patents. A utility patent is what most think of as a patent - something new or useful. A design patent protects the way something looks. These are the generalities anyway and like everything about patents can get very complicated very quickly.
From 1790 to 1835 a patent was 14 from issue date.
From 1836 to1860 it was 21 years from issue date.
From 1861 to 1994 it was 17 years from issue date.
Since June 8, 1995 a utility patent is 20 years from FILING date (not issue).
A design patent filed before May 13, 2015 has a term of 14 years from the issue date and a design patent filed after that date is 15 years from issue date.
So dating can be done within a few years if you know when it was patented. Sometimes patent numbers are not on something or were put on before the official patent date but it gives a pretty good approximation of era.
The US patent office also offers a service
https://www.uspto.gov/patents-application-process/search-patents I should say they offer a free service.
This is all for US patents. International patents is a whole different can of worms.
