3 Cent !918 Washington #502 ID Help

Hello

Over the past couple of months, I've been going through some of my old purchases from estate sales and auctions of which I found many early 19th century postcards. This activity has now given me the fever to know more about stamp collecting even though the more I read the more complicated it gets. I have a question about these two stamps. The one on the left looks to be possibly a Washington 1918 #502 and I'm uncertain about the one to the right which is has a variance in color and detail. Any help would be appreciated.

Have to checked the perforations? If so, what did you observe? Have you determined the printing type (flat plate, offset, etc.) of the one on the left? These are the two things you should determine to start your identification process.
http://stampsmarter.com/1847usa/was...d33perf.html
Don

Thanks for the information. Both stamps are a perf 11. Based on the link to the website sent earlier, I believe the stamp to the left is a flat plate type I and the other an offset type III that was never used but placed on a card and never mailed. The new stamp posted here is on an 1918 postcard and I believe to be a perf 11 type II.