FELT MARK
Imprint left on the paper by one or more of the felts used in making the paper. The mark may be wanted or unwanted and special effects can be introduced in this way.

FIBRILLATION
Freeing of the fibrils by partial rupture of the fibers when submitted to an appropriate treatment, e.g., beating or refining.

FILLER
A material such as china clay or calcium carbonate that is added to make paper smoother and increase opacity.

FILLING IN
The addition of components of the furnish of a paper to pulping or slushing equipment in a paper mill. The spreading of the printed image on a sheet to the point where the small unprinted spaces are obliterated.

FINES
Small fragments of fibers produced, for example, in the course of beating or refining.

FINISH
The surface characteristics imparted to paper by mechanical means.

FLAME-RESISTANT PAPER
Paper that has been given a treatment designed to give it a certain degree of non-flammability and/or of incombustibility.

FLOW BOX
A container for stock situated immediately before the forming part of a paper or board making machine, capable of supplying stock in the required volume and with the required distribution characteristics to the forming surface. Also known as the breast box or head box.

FLUORESCENT WHITENING AGENT / FLUORESCENT DYE
A dyestuff capable of converting ultraviolet light into the visible spectrum and improving the brightness of the paper in which it is incorporated. Sometimes known as optical bleaching agent (OBA).

FOILS
Static bar-like devices situated below the forming wire of a papermaking machine to assist drainage of water from the stock.

FOLDING BOXBOARD
Although boxboards can vary in quality from gray board to high-class board made from virgin fiber, the term is usually taken to mean white-lined boards. They are made on multi-layer machines, and the outer layers may be of a different furnish to the center layer.

FORMATION
The manner in which the fibers are disposed in the sheet as determined by the look-through.

FOUNTAIN ROLLER
The roller on a printing machine that initiates the supply of moisture to the damping system.

FOUNTAIN SOLUTION
Water, with additives, for application to the lithographic plate on a printing machine.

FOURDRINIER MACHINE
A papermaking machine that forms the paper in a continuous sheet. Named after the Fourdrinier brothers who financed the first operational machine at the Frogmore Mill, Hertfordshire, England in 1803.

FREE STOCK
Stock that, when drained under gravity, parts easily with the water of suspension.

FREENESS VALUE
A measure of the drainability of an aqueous suspension of stock, determined and expressed as specified in a standard method of test.

FURNISH
The ingredients or constituents of which the paper is made. Fibrous furnish concerns only the types and proportions of the fibers present. Total furnish includes loading. etc.