First they often use very opaque, bright colors not found on earlier marbles, and second the clarity of glass is usually much superior to earlier marbles. It has been postulated that this is due to the use of gas fuel instead of wood in the furnaces. All these marbles have either a very rough pontil or a factory fire polished surface that has smoothed over the pontil. Types of marbles more commonly seen in this later period include Joseph Swirls, single color Solid Core Swirls, crudely made blue and green glass Swirls, Banded transparents, and all varieties of swirls. This has been a very short overview of a complex subject which has not been given enough attention in the past.
Any comments are very welcome.