You could have a look at somewhere like WEX as they offer a huge variety of worktop woods that are also great for using as shelving.

They can cut to order from the main pieces and supply Danish oil to coat them to help avoid staining and bring out the beautiful colours: http://www.worktop-express.co.uk/solid-wood-worktops

Tying the same wood into other parts of the kitchen (ie some exposed shelving in the units or a breakfast bar) can work really well.

Here's a recent design I'm working on matching the breakfast bar to the shelving in the corner if that helps show what I mean:

In terms of strength, they are available in 40mm thickness so easy to support either internally for floating look or externally with brackets. They're definitely good enough themselves to support stacks of plates though.

You can definitely have floating shelves that will support plates but they will need to be fixed to the timber frame (you can use a stud finder to tell where the wood is for fixing).

I am still worried though. Visions of CRASH IN THE NIGHT.

I think if i were supporting something very heavy ( and the shelves give and indication of max weight on the boxes ) I'd be tempted to go right through the stud wall to the brick/ block behind and use bolts long enough. Floorboards will not work on their own, they're not thick enough, they'd need a support underneath.

You'd ideally need to go for something a lot thicker to get the bolts in the middle and avoid mishaps! Something like a 7"x3", you can still get something that looks aged from a reclaimed timber yard. However, I would point out that most dinner plates are standard 10" across, so you need to bear this in mind too, as a timber to put them on would need to be 12" by 3 or 4" I'd suggest that maybe it would be better to build a structure from reclaimed timber that had supports either end that went to the floor or the counter top at the very least.

Thank you MATH.

That helps explain why so many "floating shelves" are so thick. The shelves themselves must be very heavy too, if of reclaimed timber.

My stud walls have the added complication of insulated plasterboard. I am beginning to wonder if floating shelves are actually a bad idea in my case.