According to antiquebottles.com website, Milk bottles before the 1930s were normally a round shaped bottle with a wide collared mouth. In the 1950s, a square squat bottle became increasingly the more popular style. Milk bottles since the 1950s have used pyroglaze or ACL (Applied Color Label) to identify the bottles.
Before the 1960s, names were embossed in the glass on milk bottles. The name was debossed on the slug plate, then the plate was inserted into the mould used to make the bottle - the result was the embossed name on the bottle. By the 1960s glass bottles were replaced with paper cartons.
Milk and cream bottles often were registered and had a unique registration number embossed underneath. Often a suburban dairy or dairy business had their own embossed milk bottle, or a pyro-glaze version, sometimes with additional advertising for other local businesses on their bottles. These are often quite scarce.
Western Australia has quite a number of embossed and pyro label milk bottles to collect. The range includes large dairies such as Masters and Peters as well as small suburban farm dairies which lasted only for a few years before closing or being bought out, and whose bottles are highly sought after.