These three Whistle buttons are made of Composition which to my way of thinking is a mixture of left overs like sawdust, stone filings etc. and some type of glue with I imagine some type of hardener to set it. A Whistle button has one largish hole in the front with two holes in the back and that enables you to sew on the button and the thread is down in the hole and can’t rub or wear out. Do I sound like I know what I am talking about cos I am trying!! Apparently in the old days there were small whistles that were similar to these buttons, hence the name.