Jam Gone Wrong

A few weeks back we had a go at making a batch of plum jam.  All went well, but once jarred it clearly hadn't set and all looked too sloppy and syrupy.  Right, thinks I some time later, I'll put all the jam back into the pan, add some more jam sugar, boil it and jar it, that's sure to make it set.  And it did!

And there's four jars just like this, filled with ultra-dense super-sticky sub-organic matter! Anyone need some grouting done? Some homemade No Need For Nails?

Now I need to figure out how the deuce to get this... stuff out of the jars - I fear industrial solvents may be required. At this rate I'll never make it into the WI...