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Text 3 Proofing

Once film has been made, a proof has to be produced so that the client and reproduction house can satisfy themselves that the quality and sizing are correct and the printer, too, will require a proof to refer to when printing the finished job. Proofing can be done either on a press or by using photographic/electrostatic methods.

Press proofs are produced on a special proofing press. This is in essence an offset printing machine, which usually prints one or two colours at a time, with the "paper fed in and taken off by hand. Before proofing, an offset plate is produced in the normal way. This may be a plate specially made for proofing, or can be the same plate that will eventually be used for printing (a machine plate).

Proofs of four colour process work should include a colour bar; this is used by the reproduction house, client and printer to check the density of colours on the proof. There are various standard, colour bars, all of which enable the ink density and other factors to be read by use of a colour reflection densitometer (a device that reads the density of colours). The printer can therefore set the ink density on the press to be the same as on the proof and this can be measured accurately by meter rather than merely judged by eye — or set automatically where suitable press controls are fitted.

'Progressives' are produced when proofing: these are proofs of one, two or three of the four colours and show how the eventual proofing result has been achieved.

An alternative to press proofing is the use of photographic/ electrostatic methods (Dupont Eurostandard Cromalin and 3MMatchpnnt are two common brands). A Cromalin is made by exposing each separation film on to a sheet of photosensitized clear plastic. This sheet is treated so that ‘dust‘of one of the four process colours will adhere to the image areas. The four plastic sheets (one for each process colour) are superimposed in register and laminated for protection. This form of proofing is cheaper than press proofing when just one or two proofs are required, but more expensive if more copies are wanted. Cromalins can only be one-sided.

Straightforward black-and-white halftones are normally proofed as ozalids or photographic bromides. However, for high-quality photographic work it is advisable to have press proofs on the correct paper.

Checking colour proofsWhen the client receives colour proofs they should be checked for sizing (normally done by the designer) and colour quality. As well as the actual colour values, it is also important to check for blemishes, scratches, process stains and broken screens (a magnifying glass helps here). Register (the correct positioning of the films, so that the dots are in the correct position relative to each other) must be checked: a subject which is out of register will look fuzzy and slightly out of focus. A more serious problem is where the colours are 'out of fit'. This means that, during reproduction, the films have become the wrong size relative to each other. Bad fit can usually be corrected only by rescanning.

Colour separation is probably the most complex area of printing technology, so it is best, when in doubt about colour correction, to get staff from the reproduction house in to discuss the problem.


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