craftgrrl | Strange request. Need crafty help.

Some of you ladies may remember the post I made a few weeks ago about the nursery I made for my son.
The one with the mobile made out of sticks and paper cranes.

Well, last Wednesday my son died. Just 1 week after he was born.
The experience has been one of the most excruciatingly painful ones I've ever been through, and I'm doing what I can just to get out of bed in the morning.

The reason I'm here however, is because we're having him cremated this week, and I'd like to take some of his ashes and have them made into a necklace.
I was thinking of mixing them in with some clay, and making a pendant.

The only thing is that I have no idea where to start.
I don't know what kind of clay to use, or how I would fire it without a kiln.
I don't want to use air-dry clay because I figure it won't be sturdy enough and I need it to last a lifetime.

Any tips or advice would be greatly appreciated.
Or, if you think I should skip the whole clay idea in general, in lieu of something that would work better to preserve some of his ashes, I'd love to hear it.
I just really want to craft something, because it was my craftiness that I was most proud of sharing with him, and hopefully passing on.

I'm also going to take some ashes and mix them into some paint and make a painting.
I was going to use acrylics, but if anyone knows of a better paint to use, I'd love to hear that too.

Thanks in advance ladies.