mike wrote:

I have a good quality and quite old shovel which has serious layers of
all sorts of muck - including old cement - very securely stuck to it.

Any suggestions for cleaning - other than a cold chisel and hammer?

Wire brush in an angle grinder with eye protection, gloves and heavy
duty clothing.

After it is clean store it in a bucket of dry playground sand which has
clean engine oil added to it to make a paste. Don't use old engine oil.