The Colour of your Ink can influence your Printed Results

CMYK or process colour printing should be as easy as pie, because if you are using straight process colours the variables are greatly reduced - right? Wrong!

There is no such thing as a standard CYAN. You cannot go down to your local standards office, open the big safe and find a tin of standard Cyan inside.

Valuable production time can be lost due to the colour of ink the just not being right or not suited to job at hand. Other things can combine with this, such as, substrate type and using the correct colour measurement instrument and settings.

Let’s have a look at the key points to check in the press room.

Check the Ink

For process inks, especially if you are printing offset sheet fed or heat set web to ISO 12647-2:2013 your inks should meet ISO 2846-1:2017, as a start. This is a normative reference in 12647-2.

For special colour inks a draw down sample from your ink supplier is a good place to start. Even better if this is done on the substrate you will print with.

The draw down can then be measured and the spectral data incorporated into your colour analysis and reporting software (e.g. Mellow Colour Print Spec or Ink Spec) as an in-house standard. If the draw down is supposed to match a ‘library’ colour you can use the in-house measurement data for reporting through your internal quality dept and for improving the match through further discussion with the ink supplier.

Either of the above is really required otherwise you will be flying blind, so to speak.

Check you are using the right instrument

You should be using a spectrophotometer with 0/45 or 45/0 illumination. This is the standard geometry instrument that suits most printing and packaging applications. Some highly glossy flexible materials, metallic inks and gold or silver foils may require a spherical spectrophotometer.

These types of materials will not measure the same way that we see that colour when using a 0/45 or 45/0 instrument. A spherical spectrophotometer can be set up exclude or include the gloss component - excluding the gloss can provide an improved visual colour match depending on the material being measured.

See the sample diagram below.

Check your instrument measurement settings

Make sure you are using the same, and correct, settings for the illumination and observer according to the standard. Most colour standards will specify D50/2 degrees - some brands and paper manufacturers may use D65/10 degrees. Check you are using the same illuminant and observer as specified.

Check your measurement mode

This is like choosing a filter setting in your spectrophotometer. The latest ISO 12647-2:2013 specifies M1 mode, to adjust and allow for the increased use of optical brighteners in substrates today. You may have been or are currently using M0 mode which is the older ‘legacy’ setting for most older instruments.

Check what is specified in the standard. Changing to M1 can mean a lot of re-measuring standards etc. But it is worth it in the long run. Other modes are M2 (UV cut) and M3 (Pol filter).

Check your Backing

When you measure a thin or slightly transparent substrate you should always use the correctly specified backing material, underneath the substrate to be measured.

Black backing ensures there will be no influence of what is underneath the sample or printed on the other side. White backing is the standard for measuring digital proofs.

If you print flexo, and / or just print on one side, white backing will be fine. And, there are ISO standards for backing.

Check your dE (delta E) setting

What dE tolerance method should you be using? What is specified in the standard? ISO 12647-2:2013 uses CIELAB dE or dE 76. Many print buyers and brands are specifying dE 2000. Make sure you are using the correct dE according to your job and standard.

Check your measurement and reporting procedures

Measurement of printed samples and reporting should have a clearly defined step by step procedure. This will Measurement of printed samples help avoid mis-reads of samples and strange report results appearing randomly. A procedure or set of procedures should be available to all who are responsible in the colour workflow. These are sometimes called standard operating procedures (SOP’s). A set of SOP’s also enables new staff to be trained correctly and effectively.

Check the measurement data source

Target L*a*b* values should be created from spectral measurement data. L*a*b* values require reference information, such as;

a) illuminant and observer (e.g. D50/2 degrees)
b) Type and Specification of Backing (White or Black)
c) Measurement Mode (M0, M1, M2 or M3)
d) Instrument Geometry, Instrument manufacturer, model, etc.
e) Instrument certification (up to date?)
f) Instrument aperture size (2mm, 3mm or ?)

Straight L*a*b* values with no reference data will have no meaning and cannot be used to accurately communicate colour.

As you can see not all colour measurement is equal. Care and attention needs to be taken when measuring standards and samples!

For more information about the benefits of using a Colour Spectrophotometer training and the TECHKON instrument range please contact us at info@colourgraphicservices.com