Shoe buckle frame ? Large button ?
Not a button IMO.The problem I have is that there is no shank
Here take a look
View attachment 1914968
View attachment 1914970
If you're convinced this isn't a button, then possibly a colonial horse rosette?
"In modern times, the rosettes became commercially popular after the mid-1800s and continued in common use until the automobile replaced the horse-drawn vehicles in the early 1900s. However, they are still manufactured and used today. Sometimes mistaken for a button, bridle rosettes were designed first and foremost as a handsome decoration. However, in some cases they served to hold the crown piece and browband together on a riding or driving bridle. Today, horse rosettes are most easily identified by a large rectangular shank through which the bridle strap passes to hold them in place. They have been made with a wide variety of materials including glass, leather, rubber, celluloid, jet, silver, and other metals many of which can be seen below. The most popular today are those with a domed or flat glass cover set in a metal frame. Many have paper cut-outs under the glass to simulate a border and to provide the display of a picture, symbol, letter, or number. Rosettes were made in a large variety of pictorial designs and many identify a person, a family, a horse, or a story. They were also used by the Federal Calvary during the Civil War and later by certain civil-mounted police. Over time, many companies used the rosettes as advertising tools."