If you put something in the bottle with the hide glue to keep it upright in the water, don't use steel. Oxidation of the steel in water will turn the glue black, and cause it to leave a glue line that is usually visible. Stainless steel will not cause this. So use a stainless ball bearing or, easier to find, a couple of stainless nuts or screws. Clean them in alcohol before putting in the glue, to remove chemicals used in manufacturing and cleaning.
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