How do you make icing for cookies? and is it ok to make in bulk? how would i store it? and for how long is it good for?

I typically make a double batch of royal icing and store the extra in a air tight container. I usually leave it out on the counter for about a week or so.

As long as it's not colored, I've been successful with storing RI in the freezer for extended periods.

I always use glace icing (powdered sugar, corn syrup, skim milk). By using the same proportions, I can make as little or as much as I want. The leftovers can be refrigerated for up to two weeks. While the icing is still okay to eat after that, the finish when it dries isn't always blemish-free! Has a tendency to spot.

So I can't find a recipe for glace. I put that into the search tab and it said nothing was found! WTH? Can you tell me what your typical ratios are for glace, please?

Thanks!

EDIT** Nevermind! I found it...helps if I spell it correctly! I was spelling it using a "z" in glaze instead of a "c". What do you thin it with if it's too thick--milk or corn syrup? I want these to set up so I can put them in a cookie arrangement.