What is the term for a material that is used to obscure information on a transparency?

The term for a material that is used to obscure information on a transparency is opaque material. Opaque materials do not allow light to pass through, making them effective at hiding or concealing the information underneath when applied over a transparent surface. This characteristic is particularly useful when an instructor wants to selectively highlight or mask certain information during presentations or demonstrations.

Transparent film, on the other hand, allows light to pass through and is used primarily to display rather than obscure information. Reflective surfaces redirect light but are not specifically designed to obscure information in the same way. A colored overlay may change the appearance of the information but does not completely obscure it, as it still allows some degree of visibility. Thus, opaque material is the most appropriate choice for obscuring information on a transparency.