Up until 1948 what was the shellac of record albums made from?

Five years later, in 1895, [Emile] Berliner introduced discs based on shellac - a resin secreted by female lac bugs, mixed with clay and cotton fibres. This brittle and inexpensive composition dominated the industry until the early 1950s.

...the most commonly cultivated species is "Kerria lacca." These insects secrete a waxy resin that is harvested and converted commercially into lac and shellac, used in various dyes, cosmetics, food glazes, wood finishing varnishes and polishes.