stone sealing

It goes a very long way and does the job properly. Try a couple of decent tile shops - I think you can get it in 250 and 500ml tins but obviously more expensive pro rata.

Certainly can.

The traditonal way to get a "natural look" to stone (or anything) has always been to do nothing at all! If "sealing" has any effect at all it will not look natural, by definition Waste of money

Not really, here's why.

The 'traditional' treatment for slate which is exposed to dirt, either in the form of food in the kitchen, or soot on a hearth, is to seal the slate with either milk or wax.

If you don't do this, the slate gets very messy very quickly, and is a bugger to clean. If you scrub at it, you leave scratches, and it really doesn't look good.

However, sealing in this way leaves a shiny appearance, which may not be the desired effect. Fortunately, we now have silicones at our disposal. These are great, because you can use them to impregnate a permeable material, such as slate, down to a thickness of a couple of mm.

This leaves the slate looking exactly the same, while making it strongly hydrophobic - it repels water. When you next spill some red wine on your slate floor, it won't soak in, it'll just wipe off.

If it wasn't for a WBS then I might go with that. The alternative is black limestone.

No it isn't. The whole point of using MN Stainstop is that there is little or no change to the appearance - specifically the stone will remain looking very "flat" indeed. I'm extremely picky about things looking natural and this achieves it while preventing the stone from becoming grubby and non-cleanable.