Zwanzig, K.wurtt.post

Hi Everyone,
I tried to search for this stamp here on SCF, using the key word 'zwanzig' with no results. I tried looking through my Scott Catalog, but only found some others with the K.Wurtt.Post, but did not have the ZWANZIG on it, so I have no idea about this stamp except that it is lovely and even the backside is pretty interesting with it's "crackling" like look.

Is the back supposed to look like that?
What year is this stamp and the Scott number?
I want to get as much information before I auction it off. I even tried looking on ebay but obviously I don't know what I am doing
Thank you all so much, here are the photos:

Try the German state of Wurttemberg before Germany in Scott . Zwanzig is 20 in German. Hope this helps. Bernie

Yup. It appears to be an 1875-1900 Wurttemburg stamp. Scott #61. 2008 catalog value, Mint is, $1.00. 25 years is a long time for one stamp issue to be printed and used.

Thank you all so much for the information.
It will help so much.
What about the backside?
Is this common looking?
Much appreciated!
Sue
(SueStamps)