OBA is the abbreviation for “Optical Brightning Agents” or optical brighteners.
Optical brighteners are additives that are used by paper manufacturers to make a paper look white and luminous.
To make a paper look white, it is important to add substances that shift the invisible ultraviolet spectrum between 320 and 400 nanometers into the visible range from 400 nanometers onwards. The paper is thereby bluish or fluoresces in areas that are just visible to the human eye so that our eyes perceive that as a brighter, bluish white. Color measurements are so easily corrupted by optical brighteners, for example, created profiles could be yellowish, because the meter is trying to correct the blue cast of the paper.
Many “white” papers have optical brighteners in it. Sometimes, the brightening effect will weaken over a relatively short period of several years, as the whiteness of the paper will vanish over time.
Optical brighteners are additives used by paper manufacturers to make a paper look whiter and brighter.
To make a paper look whiter, it is important to add substances to the paper that shift the invisible ultraviolet spectrum between 320 and 400 nanometers into the visible range from 400 nanometers. This makes the paper bluer or fluoresces in areas that are just visible to the human eye. While our eyes perceive this as a brighter, bluish white, a colorimeter only sees a different blue. Thus, the colour measurements are slightly falsified by the optical brighteners, the created profiles could be yellowish, as the measuring device tries to correct the blueness of the paper.
Many “high white” papers have optical brighteners in them. Partially, the brightening effect weakens over a relatively short period of several years, thus the wisdom of the paper decreases.
Offset printing is an indirect printing process.
Indirect means that the printing plate and the substrate do not come into direct contact with each other, but a medium in between is used as a transfer medium.
It is the most widespread printing process.
– sheet-fed offset printing machines and
– Web offset printing machines.
An online proof (correct: contract proof) is an ISO-certified testing device for the graphic arts industry. The word online proof is usually used in the context that the proof is ordered online, i.e. via the Internet.
An online proof simulates the colourfulness of offset or gravure printing in a colour and legally binding manner within the narrow tolerances of ISO 12647-7. Today, it is almost exclusively calculated via a RIP and then produced with inkjet printers on special proof papers.
The proof data is converted into separations, then reassembled into a composite image to correctly simulate overprinting and trapping. The data is then transferred as a newly created composite image to an inkjet printer, usually with more than 8 colours, which prints the data. In addition to the print data, a proof must also carry a UGRA/Fogra media wedge in order to be color-consistent and legally binding. Thanks to the standardised wedge, the printer is able to check the proof for correctness. Since many printing houses do not have this measuring technique at hand, the proof is often provided directly with a test report that shows the correctness of the measured values of the media wedge directly on the proof.
Earlier methods such as Chromalin etc. are no longer available on the market today.
In addition to the term “proof”, terms such as colour proof or digital proof are also commonly used.
ISO 12647 defines the term “Validation Print” (ISO 12647-8) in addition to the highest standard of contract proof, “Proof” (ISO 12647-7). The Validation Print is characterized by the fact that although it is less accurate in color, it can also be produced on laser printers. Compared to the contract proof, however, it accepts much higher colour deviations and is only legally binding after prior consultation. A real “proof”, i.e. a real contract proof according to ISO 12647-7 is currently not only by far the best variant in terms of colour, but also the only legally binding proof.