What happens if you mix hydrated lime with Plaster of Paris? (Making frescos with kids)

I'm teaching kids about the ancient Minoans, and thought it would be fun and educational to have them make their own frescos. I have bagged plaster of Paris and hydrated lime on hand. A lot of the instructions online say to just use plaster of Paris. This stuff sets super fast, which kind of defeats the purpose of fresco painting .

With traditional buon fresco, you're painting with pigments on wet lime plaster. As the lime sets, it also sets the pigments in stone, making them last a lot longer. You usually have a few hours paint, so you only apply enough plaster that you can paint in one sitting.

The plaster of Paris sets in like 5 minutes. I also found it was really hard to add paint to--it didn't really absorbed, and it also sometimes wicked the paint along the plaster. Not optimal. But, lime plaster is expensive and very alkaline--not too good for use with kids.

I did a quick google search, and AI told me, "Mixing hydrated lime with Plaster of Paris (gypsum) creates a durable, workable "gauged" lime plaster, often used for smooth interior finishes. A common, strong mix is 50/50 by weight of both ingredients, with water added to reach a cream-like consistency. It sets faster than lime alone" This was actually taken from this permies thread.

I figured I might as well give it a whirl and see how it worked out. I eyeballed a 50/50 mixture and added about half as much water by volume. The resulting mixture was:
(A) Easier to smooth
(B) Took quite a bit longer to set--more like 30 minutes. Perfect for a classroom activity.
(C) Absorbed the pigments a lot nicer--no wicking or running of the paint
(D) A bit more resilient: the 100% plaster of Paris really pushed down when I applied the brush. The lime/gypsum mix was more...elastic?
(E) The colors are shinier! The painting just looks a lot more vibrant. Both my kids thought it looked better than my 100% plaster-of-Paris version.

I'm not sure how durable each one is. They're just applied on burlap, and both are pretty easy to crack. I feel like the 50/50 mixture is currently easier to crack, but it's also thinner and it still feels a bit damp (it's going to take longer to set, I'm sure!)

I'm mostly posting this to document my little experiment. But, if anyone has any ideas or input or experience with these mixtures, I'd love to know more!

Here you can see an example of someone else trying to make a fresco in Plaster of Paris. The pigment really doesn't want to apply, and it impressed deeply with each brush stroke:

Hmmm, it's been a few hours. I picked up both frescos to show my husband. He agreed that the 50/50 mixture was far nicer. But, even just holding it gently to show him, the 50/50 mixture cracked. It is thinner than the 100% Plaster of Paris, so that might be why. Or, is it that the lime is still setting?

I wonder what a 25% lime/75% plaster would look and work like?

I thought, "Why not try another test!?" So, this time I did 1/3rd lime and 2/3rds plaster. (1 tbsp lime, 2 tbsp plaster, a little over 1 tbsp water). I also laid it on a little thicker.

It seems that this mixture retains the benefits of lime. The paint and plaster are still shiny, and there isn't frustrating wicking going on. It might have been slightly harder to work with than the 50/50 mixture. It didn't seem to dry too fast, but it might have dried faster than the 50/50 mixture. I was able to finish my painting before it had solidified.

It should be less alkaline (so better for kids), and hopefully will be more durable. I also have a lot more plaster of Paris than I do hydrated lime, so this should help stretch the amount.

We'll see how they all look in the morning. I'm going to try to be good and not mess with them until then.