Procedures for reusing inks with the integrated spectral data method

A step-by-step guide to reusing leftover inks that cannot be blended with the standard ‘mathematical’ method…

Reusing inks left over from a production run is a must-do for packaging printers seeking to cut ink spend, improve efficiency and meet sustainability targets.

The recommended and most efficient method of reusing flexo or gravure press returns is the ‘mathematical’ method, where inks get calculated into a formulation of precisely weighed ingredients. However, this only works when the ingredients (like pigments) of the press return inks and the target colour are similar – and known.

Why printers face pressure to reuse leftover inks promptly

In certain situations, printer can’t rely on the mathematical method to reuse leftovers. Once exposed to the atmosphere, ink shelf-life reduces, so it’s not in the printer’s interest to have leftovers sitting around for long. Suppose you have a high number of batches, or returns with widely varying pigments? The printer faces pressure to remix these returns into new jobs before they expire – in extreme cases, all at once. Furthermore, contaminated inks can never be reused mathematically.

Thankfully, there’s a back-up method for using these types of leftovers, known as the ‘integrated spectral method’.

Inventories of returned ink, stored for eventual re-use, at a label converting factory

What is the integrated spectral method for press-return inks?

The spectral method involves using spectral data from leftover inks to create a recipe of a new target colour that comprises both return inks and fresh inks. Many printers employ this technique, utilizing a “stand-alone” spectrophotometer and colour formulation software. However, through the integration of colour formulation software with GSE Ink management software, you can capture ink logistics details such as stock, cost, and traceability data.

A step-by-step guide to the integrated spectral method

1. Identify, measure and select return containers based on spectral data

  • Determine the CIE L*a*b* coordinates of the returned inks with a spectrophotometer. Store these coordinates along with the return-inks’ container IDs in the colour formulation software.
  • When you receive a new order, get the colour target information, expressed digitally, in CIE L*a*b* coordinates (e.g. by scanning a sample to determine the colour target in colour formulation software, with a spectrophotometer).
  • Select these coordinates as the target colour, in colour formulation software. The colour formulation software shows all the available return containers in storage, plotted on a CIE L*a*b* colour-space diagram, in relation to the target colour. The target colour is at the intersection of the x and y axes, in the centre of the diagram. The colour difference grows the further you go from the target. It is possible to see, at a glance, the deviation of the return inks from the target, in DeltaE terms.
  • Note the return container IDs you want to use for the new target colour.

2. Collect returns in one container

  • In GSE Ink manager’s Return formula dispensing software module, select the target colour.
  • Select and collect the desired containers of return inks to make the target colour.
  • Blend the ingredients of the return containers. Some of our customers add fresh ingredients (like a varnish or solvent) at this stage, using the ink dispenser.
  • Print a label to identify the dispense container.

3. Adjust container

  • Formulate the recipe of this blend with the help of a spectrophotometer and the colour formulation software.
  • Import the colour correction with the help of the GSE Colour connect software module.
  • Dispense the additional fresh colours and other ingredients to reach the colour target.
  • Measure the colour of the resulting blend.
  • Then, make a correction if necessary.
  • The container is then ready for production.

The colourist’s approach
In some printing companies, experienced colour experts can visually determine which press returns can be used to achieve new target colours. This means they might skip some of the colour measurement steps described above. However, when it comes to the final “adjust container” step, they usually rely on colour measurement tools and software.

Best of both worlds

In certain situations, employing spectral data to use “challenging” press return-inks in new dispensing jobs perfectly complements the efficiency of the mathematical approach.

By combining colour formulation software with GSE ink management software, you get the advantages of both methods. This allows you to recycle every bit of leftover ink while also keeping a detailed record of all ink logistics events.

If you need more advice on how to optimize the reuse of press-return inks, and for all ink logistics enquiries, contact us at