How do you tell if a brooch is worth anything?

[dracoskip]

I have a few brooches in the bag of jewelry I'm sorting for a lady..and I have NO idea how to tell valeu, age or anything.  I am hoping for assistance.  I don't have much info because I just don't know about them, and I would hate to tell her bad info..and not sell her stuff for the best she can get out of them.  

Here they are..

The boquet one is missng a stone, but we have the stone   no markings anywhere I can find.

The red one has no markings that I can find either

The turtle.I think is modern, but, I have no knowledge of brooches.  

How do you tell?  I think the red one is the oldest..but that is just my guess....and without any marks that I can see anywhere I can't even tell what they are made of...

[impiusgems]

I usually start by doing a google search of  say for instance "art deco frog brooch".  That will usually get me started in my research.  There also resources for dating old pins and brooches by clasp type.  

Here are a couple.

https://www.realorrepro.com/article/Dating-brooch-fasteners

https://www.myclassicjewelry.com/blog/vintage-jewelry-hardware/

Hope this helps.

[debora_34_]

That's very good direction.  I just want to point out though that your frog pin is not art deco in design.

Debora