Re-using return inks by the ‘cluster’ method

Collecting leftover inks of similar colours in one dispensing barrel offers maximum recycling efficiency for wide-web converters

The standard way to reuse press-returns is to store the leftover ink from each printing station in a dedicated container – normally a bucket – until it is recalled for the next suitable job.

However, converters consuming large ink volumes can save space, handling and administration by ‘clustering’ their returns. ‘Clustering’ is when leftover inks with a similar colour are collected together in one large barrel. The barrel is then connected to the ink dispenser and treated as a base ingredient in new ink recipes.

This method can be used in addition to, or instead of, the individual container method. It is suited for wide-web converters serving markets such as paperboard products, flexible packaging and wallcovering – and situations where large amounts of a special brand colour are consumed.

Setting up and maintaining a cluster return system:

Here is a guide to help you decide if the cluster method is suitable for your business – and essential steps for adopting it smoothly in your schedules:

Step 1: preparation: checklist of essential equipment and software
First, check that your organization possesses the following essential equipment and software:

  • Ink dispensing system with available connection for extra base component
  • Collection barrels (e.g. 200L drums or 1,000L containers) that are capable of being connected to the ink dispenser.
  • A filter, fitted in the supply line to the dispense head, to remove impurities in the returned ink
  • A spectrophotometer with colour formulation software
  • Ink management software with a module for managing the reuse of clustered inks

Step 2: determine the colours for clustering
Determine which ink colours can be clustered. These should be different shades of the same colour or similar colours. Focus on your long-term output needs: what spot colours do you print frequently? The clustered inks must be a useful ingredient for making colours that will be printed in large quantities. Remember: this cluster will form just one base colour for dispensing along with others – it is not a target colour!


  • If you supply a major cola drinks brand, then limit the collection to red shades – from light to dark.
  • If you’re doing regular runs of cardboard fruit boxes for oranges and clementines, collecting reds and yellows together is acceptable.
Step 3: select return ink containers and create the cluster
Using your ink management software package, select the containers in your return ink storage that match your criteria in step two. For example, the software can help you to collect all the containers with the same base ingredient – or the same combination of ingredients. Retrieve the return ink containers from your storage, and pour them into the designated barrel. Be sure to cluster all the inks you’ve identified for this process before proceeding to the sampling stage.

Some printers create clusters by throwing returns with a certain colour shade into a collection barrel, as soon as they come back from the printing press when the job is finished. Using this alternative method, it is no longer necessary to book in the individual containers into the return ink storage before collecting them. This saves time and storage space.

Step 4: sampling – to get the colour and formulation references
Take a sample of the cluster and measure its colour using a benchtop spectrophotometer. As well as providing digital colour references, the colour formulation software (CFS) that comes with this device will provide the formulas for making the cluster’s colour. There can be even more than one formula!

Having multiple ink formulas will help you use the cluster for more new colour formulas and enable faster processing.

Each formula for the cluster is called a ‘cluster index.’ With GSE Return ink management software, you can allocate the different formulas to each cluster.

Suppose we have created a barrel containing a special red colour. The CFS provides two formulas: a combination of red, yellow and varnish (‘index 1’) and a combination of a special ‘Christmas red,’ white and varnish (‘index 2’).

With multiple formulas, there are more opportunities for reusing the clustered ink to achieve maximum recycling efficiency. In the above case, five base ingredients in formulas can be used to form the cluster colour.

Step 5: connect to the dispenser
Now the colour and formulas of the cluster are identified, the barrel can be connected to the ink dispenser.

Step 6: using the cluster in new jobs
The operator has control over whether to use clustered inks in new jobs – or not.

By default, the software is set to automatically use clustered inks for making new spot colours. However, on request, the software can be configured so that clusters are only used with the operator’s consent.

When it is used, the cluster is treated just like any other base ingredient. The software calculates the quantity of each ink ingredient needed for the new formula, using the mathematical method discussed previously. And then, the new job is dispensed.

Note that some brands do not accept the use of return inks in their jobs. To ensure compliance in these situations, GSE’s software lets you program selected spot colour formulas to contain only fresh inks.

The cluster method can be used as well as the container method. Overall, this method enables converters handling large ink volumes to reuse press return inks faster and more efficiently, than by using the container method alone.