I prepared last night by filling tubs of various shapes with water and putting them in the freezer so they would be ready this morning. We covered the table with old towels (this proved essential once the coloured water started moving!) and tipped out the ice into a large roasting tin with high sides.
This was Harry listening to try and hear cracks forming in the ice (he didn't hear any)
We could see the colours under the top layer of ice.
We could see and feel ravines down the sides of the ice blocks where the salt water had run off the top of the block.
We saw that the ice had started with smooth sides and became very rough and even sharp in places. I took a couple of the pieces out to make more space for spooning salty water back over the blocks and put them in the sink. We saw that these pieces became smooth again as they had been exposed to warm water without salt.
This was a very popular activity - Harry and Peter were both absorbed in this for over an hour. We eventually got a hole in the smallest piece of ice all the way through and Harry started chipping the blocks to try and make more holes so we stopped at this point as ice chips and coloured salt started flying around. We talked about how scientists investigate and that they might change variables in experiments so we thought what we could do differently.
If we did the same thing again (which I think we will), we would make some thinner ice pieces so they would get holes more quickly.
I have also promised a warm day ice experiment in the garden so we can use water of different temperatures and various tools to see what we can do to the ice.