I learned all about eggshell mosaic two days ago and couldn't resist trying it out...so if you see this instructable...it means it came out pretty good :-)

Step 1: Things You Need

1 eggshells
2. tacky glue
3. foam board ( this is what i had around...you could use ply wood or any hard surface you want)
4. alcohol ink ( or water colors will do i think...i just made my homemade inks and it turned out okay)
5. varnish

Step 2: Cut and Fill Your Shape

Cut your shape in wood or a hard board. i had hard form board so i cut the shape out in my styrofoam cutter ( you can check the instructable here https://www.instructables.com/id/Table-top-hotwire-Styrofoam-cutter/)
then i applied gesso and let it dry . then i sanded it.
next apply a nice coat of white tacky glue.
take your egg shell ( first clean it ...removing all the membranes in it...else it'll not stick well)., place it on your shape and press it with your finger.
you would now have flatted it with nice cracks....fill the whole area..fill in the missing areas with a tong don't worry if it over laps the design. let it dry
now gently chip out the overlapping shells.

Step 3: Color It!

Drop a few drops of alcohol ink (i think water colors will do too). you cant go wrong here...if you think you did.. just drop the desired color in alcohol ink and you are good to go...if you check out the pictures you will see how many trials and errors i have done :-)
once you feel your piece is okay...let it dry...btw...don't forget to color the back too if it's a pendant. now fix a loop for the pendant.
varnish it and you are done! well give it a few more coats and you are done! Wear it and enjoy!