Looking for non-toxic collar

Not just 100% cotton or hemp, etc.

I want one with non-toxic dyes & a metal buckle since plastic may be harmful.

I found a company on Etsy that makes leather collars but I don't know how safe the dye is. I asked them and they said 'these collars are made of genuine cowhide leather'.

That is a tough criteria. I honestly can't think of a safe collar that also avoids any type of material that could be considered harmful. My immediate concern is that without plastic or manufactured fibers that it won't give or release in an emergency.

Please, be careful in your search that you also find something that can either stretch or break if the cat gets caught on something. It is not an urban legend that cats can die when they get caught on things and the collar doesn't give. I saw the results of it when I was in middle school. Even if the cat doesn't go outside there are things in a home that they can get caught. 

I have had good luck with BEASTIE BANDS.  They are lightweight, stretchy and have no metal buckles; they are basically foam rubber that hitches with velcro and ca be adjusted for your cat's size.  They stretch and pull off if caught on anything.  If they get caught under a leg the cat can chew them off easily.  The paint is only on the outside of the band, not against the cat's fur.  Someone on here sells them, and they are easily found with an online search also.  You will lose a lot of collars if you have outside cats, but the collars show up in your mailbox if they have tags on them.  People find them and return them.