JimL,
If I am not mistaken, the original ones were of a reddish-brown material called phenolic.
HIGH PRESSURE LAMINATED PHENOLIC
Commonly called “Micarta”, a trademark of Westinghouse. Laminated sheets, tube and rods are produced in many grades, sizes and colors. These laminates combine a base material- canvas, linen, paper, glass cloth or Nylon cloth, with a resin-phenolic, melamine, epoxy or silicone, under high heat and pressure to produce a new material with specific characteristics. These characteristics vary with the grade and its use.
GRADE L (Linen Base)
PHENOLIC SHEET
Used for precision machining and high strength applications.
Sheet Size: 36" x 48".
Sold in 6" x 6", 6" x 12", 12" x 12", etc. pieces only.
Electrical-Grade Fiberglass (GPO3)
Finish
Color: Opaque red
Temperature Range: 0° to 284° F
Tensile Strength: Excellent
Impact Strength: Excellent
Good electrical insulator
Use indoors
Machine with carbide tooling
Hardness: Barcol 50
Fiberglass-reinforced polyester combines electrical insulation properties with high strength, making it an excellent choice for electrical applications. Also known as polyester-grade industrial laminate, it is sometimes considered part of the phenolic/Garolite family. Meets UL 94V0.