Trying to turn this large seashell into a ring box -- how to make it open?

[bird catbird]

Hello everyone!

I am new to this forum, I am a beginner crafter I suppose, it sort of just happened after getting sober about 6 months ago. I love to use foam and crazy glue, and I like to paint wood, rocks, and seashells.

My lover friend is a scuba diver and found this gigantic seashell under the water with both pieces intact. I want to turn it into a sort of functioning ring box so I can pop a special question when we go on vacation together. I have uploaded a couple pictures so you can see, there is a bit of an opening in the back whe I might be able to attach some sort of hinge. The only problem is it will need to allow a bit of "give" for the part of the shell that juts out to at least be able to open it 90 degrees.

It closes pretty well but there is still a large gap all the way around. I may leave that as is and just ensure the ring is secure, but I am also imagining possibly attaching a zipper so that I can zip the shell shut. So my questions are

Any advice on a type of hinge I can buy or construct to make this shell open 90 degrees and close?

Any advice on attaching a zipper around the mouth of the shell?

http://www.craftster.org/pictures/showgallery.php?ppuser=313245&cat=500

The link above is to the pictures, this is y first time using crafts tear so please let me know if you can see them or not

Thanks so much,

Birdcat

[Antidigger]

If you intend to line the inside of the shell then the easiest way I can think of would be to make a fabric hinge: a piece of fabric/ribbon/tape, glued to both sides of the shell, if you choose carefully, the fabric will give a little to accommodate the jutting out bit.

[LimeRiot]

I was thinking a fabric hinge as well. That would probably be the easiest and would let you maintain the natural beauty of the shell. I would worry about gluing a zipper on as it might cause damage.

[steiconi]

I've seen similar shells made into boxes, they're really cute. 
They usually run a small brass U channel around the outside of each shell, then solder on a hinge and a clasp.  You could probably use the copper tape used by stained glass artists instead of the U channel.

another option would be to drill holes at the hinge end and thread ribbon or cord to make a hinge.  You could drill more holes at the wide end and tie the shell closed.