Featured Marcasite and silver necklace date

Car boot find today. It’s 24 inches long, 925 marked on spring catch, I think it’s all silver. I’m finding it difficult to date from the style, Art Deco? Any info please?
It is absolutely filthy too, especially near the catch, would it be best to clean it with a soft brush with water and soap, collect all the marcasites that fall out and re-glue them in? There’s a lot missing already. Thank you.

 

Are the marcasites only glued in? If some have come out, the rest will likely follow anyway.

 

Yes, and not very well looking at some of them. I’ve seen cruddy earrings before but never this bad on a necklace. They must have loved wearing it, probably every day.

 

I’ve looked at some earrings under a loupe that have made me recoil in horror

 

I thought that marcasite was molded into the silver, making it all one piece. Glued? That's confusing to me.

 

Faux marcasite is moulded. Actual stones can be glue or prong set.

I'd vinegar that thing or even ultrasound it.

 

I'm for it being 40's or 50's? Probably 800 silver? Germany? Random thoughts........

 

Slightly slow this morning. Read over the sterling part. Stand corrected. On my part I'd hit it fairly hard with a stiff toothbrush and metal cleaner. If the some of the marcasites fall out so be it. They would probable fall out soon anyway. Then replace them using a proper glue.

 

The grubbiest bit is having a little soak, then gloves on to scrape the worst off the back with a wooden toothpick, then toothbrush the rest. I’ve got some jewellery glue somewhere. I need to stock up on marcasites, I’ve got many items with losses.