Can I use icing sugar instead of caster sugar in a cake?

[chillipickle]

Help! Am trying to make a birthday cake for OH, and have just realised I'm running out of caster sugar.

However for some reason I have two full boxes of icing sugar. Is it just sugar, and can I use it to replace some of the caster sugar?

I wouldn't.

Do you have any granulated sugar? and a food processor or something along those lines?

No you can't. I've tried it, and you get something a little like fizzy silly putty because of the anticaking stuff in it I think. You can just substitute granulated though.

No granulated here.

I have some light brown sugar, and some dark brown (which would not be OK as this is a lemon cake), and almost enough caster sugar, so I guess I'll use the light brown to top it up.

Many thanks for the advice! Fizzy silly putty is not what I am looking for.

If you use granulated in it you can get burnt specks on cooking, it's because the crystals are bigger.