You might do a better repair job by using a matching paint to cover the spots.

I wasn’t looking to repair or paint, just preserve. Thanks.

I'd use a little nail polish.

Maybe Zinsser's Gardz. Haven't used it on plaster but it is great for locking down drywall mud & making mud a bit tougher. I would use it only on the bare plaster. It might be OK to use over the gilding. Maybe test it over gilding on the back side of the frame.

Can you post some close ups of the damaged areas?

I was told use matte Polly or acrylic on another forum. I’m currently just preserving, not repairing.

Thanks, I’ve used gardz before. It’s pretty clear.

Read here... one restorer says she uses Varathane, some seem to suggest things like rabbit or fish glue, another says they inject a thin PVA (whatever that is. lol!).

Stabilizing old plaster frame

PVA = polyvinyl acetate

That’s elmers right?

Thanks all!

Yes, conservation grade elmers. it’s hard to tell from the photos, but the inner floral border may be a composition type material and not strictly plaster. These areas are brittle and have cracked. They are pulling away/delaminating from the substrate underneath/wood frame. unless stabilized they will continue to pop off. It’s also not clear from the photos if it is truly gilded.