>but how do you date it and to what period do you ascribe it?

There's no way to conclusively date the darn things. The current assumptions of late neolithic/early BA are made by association with nearby burial mounds, which sometimes contain small 'portables'. But this doesn't prove anything in the way a radiocarbon date would.

>I would suggest that such carvings were made by pounding and grinding with stone rather than >cutting with metal.
That's pretty much what the experts say too Peter. The ones in Northumberland are mostly on sandstone, and are assumed to have been made by whacking a pointed bit of harder stone (probably andesite) with another stone. So far, only one potential stone pick has been found, at Dod Law I think. Experiments have shown that this method produces motifs that look very similar to uneroded panels out in the field. Ray Mears demonstarted the technique on the telly a few years back. There's a good example in the car park at Kilmartin house museum, and a few more in my backyard ;)

There is the occasional panel which looks more tightly finished, such as at Traprain Law, giving rise to speculation that an IA date is more probable for that particular site, as it's assumed that hard metal would have been required to get such a nice clean edge. Another example is the quarry site on Doddington moor, which looks much neater than most of those elsewhere on the same moor.

Overall, it's impossible to generalise about the date or meaning of RA. It's part of what makes it so much fun to speculate :)