Hi greenbeanchick,
I'm guessing that as you mention comics, picture frames and furniture, you have already read these
threads:
here and
here, and possibly also
here. If so then I can't really add anything which is specific to your idea.
The chances are that some if not all of the actual characters you want to transfer in this way will be registered trade marks, and so you need to check whether any of them are registered in a class (probably 21) which would apply to your finished decorated jars (are they ornamental or practical?). You can do this using the Intellectual Property Office website
search tool*, and putting the name of each character in the text search box. You can see an explanation of the various classes in
this link.
The second thing to consider is the case known as
Allposters v Stichting Pictoright which I described in the second thread mentioned above. I am not sure whether the method you propose to use for transferring the napkins to the jars would have the effect of dissolving the tissue or making it transparent. If it does, then it is much more likely that the
Allposters decision would affect you and mean that this kind of transposition could be seen as infringing.
But those caveats aside, merely re-purposing something you have bought, without any copying, should not amount to infringement of copyright.
* At the time of writing this feature was temporarily unavailable.