To prepare the screen for printing it must be taped and "pinholed". Tape is applied between the mesh and the frame, and a liquid, sort of like Elmer's Glue, called "blockout", is used to fill in any small holes. These "pinholes" are caused by dust particles blocking exposure or small amounts of oil resisting the emulsion coverage. This is why air filtration and other environmental controls are necessary for efficient and quality controlled screen making.