I am thinking that the corn syrup makes it more shiny, yes? But I have always followed the directions in Antonia74's recipe and thinned with water. Do most people add corn syrup to Antonia74's icing recipe to make it shinier? And does this affect the time it takes to set and/or the hardness of it?
Thanks for any input.

The only time I have added corn syrup was with a recipe that was egg-free because of an egg allergy. It did dry very shiny. I liked it but I could not do anything very detailed with it. I have never tried it with Antonia's icing.

I just always use Antonia's regular recipe. I love it and I think it tastes great and works well. And I think mine are pretty shiny.

corn syrup is what we use in glace icing.
i think you will find it slows down drying time and your icing will not be as hard set.

Thanks for the replies. Yes, I know that corn syrup makes the glace shiny, but I have never had luck at all (despite the help and tips of everyone on here! ) with the glace.
I like Antonia's royal, but it does dry chalkier looking and matte. I just sometimes cookies on here that look more like they are iced with the glace, but people say it is Antonia's/ I saw one person explain, a few months ago, that she thinned her Antonia's with corn syrup rather than water, so I wondered if lots of folks were doing that to get the shinier look? Maybe I'll experiment when I don't really need the cookies for anything.

Would you please let us know how it worked for you after you experiment?

I sure will. I may be experimenting this weekend.
I have a birthday and a wedding coming up at the beginning of October, so I am probably going to do a practice run of some of those cookies.

Well, one night I experimented with Royal Icing, and piping gel. The Royal was piped and dry. I painted a very thin coat of gel on specific little areas. It stayed shiny, but was sort of a pain. Let's just say it's OK for a small area of detail work, like pearls.

Every time I make Antonia74's RI, I add a tsp of lemon juice to get the musty smell out of the meringue powder (doesn't change flavor, only makes it less bitter) and corn syrup to thin it. It makes it very shiny when it dries, without changing the ability for it to dry the way it's supposed to. I don't think I've ever used water to thin it.

I only use royal for cookies and I dont' add corn syrup.

Doesn't the lemon jucie make red turn orange when using food colors? I'm all for adding the lemon juice, but wonder if it works well with colors.

I've never had a problem with lemon juice altering any of my colors, even white. There isn't enough saturation of the yellow pigment to make a difference.