Butler my hats off to you...this is one of the finest looking double breasted lapel vests that I have ever seen. Makes me want to loose weight and commission one myself
Back in the 20s and 30s, many of the best makers considered horn buttons too rustic for city suits. More formal body coats were done up in covered buttons...and, starting in the 20s, in the sleek, dense, color consistent, shiny early plastics for both formal and lounge wear.
Weldon still carries this type of plastic button, the B409. Sholte put this type of button on all of Windsor's suits and even tweed jackets that did not have insignia. The B409 does not cost any less than horn buttons from Weldon...and A&S traditionally, depending on cutter or tailor, use them on the most formal, city lounges if in a dark color.
That being said: yours are horn.
You sound strangely like Alden. Are you related or simply your alter ego?
The plastic buttons used by AS can be found in Weldon's catalogue. They are referenced as the B409s. These are virtually the same buttons used by Scholte in the 1930s. I saw them on all of Windsor's suits, even the tweed suits.
The buttons are the same price at Weldon's as their natural horn buttons. So the use of these buttons by AS is not a question of economics but probably one of tradition. The B409s work very well on certain fabrics, summer weight cloths for example. My fresco suits always take B409s.
The other classic button is the corozo, made from the seed of an Amazonian palm tree. They can be very lovely as well.
If you type "B409 buttons" into a Bing search and click images this is the first button that appears. Seriously.
Then it is followed by a variety of more buttons that have to do with autism that can be seen as vaguely offensive, but I am not sure if they are supposed to be or not.