T-shirts get washed regularly and garments get a lot of use and wear, so making sure your printed designs are durable to such demands on colour is essential.
In this blog post we’ve put together a handy colour fastness guide designed to support you in getting the best performance from your MagnaPrint® inks and offer some on-press considerations for achieving long-lasting prints that will satisfy your customers.
What is Colour Fastness?
Colour fastness is a term used to refer to the resistance of textile colourants to external effects that may change their shade or appearance during usage. Various conditions can have a role to play in causing dyed and printed colours to change and fade, from washing and abrasion from usage to light exposure and even perspiration!
Several tests are available to assess the fastness grade of prints and garments. These tests evaluate samples against any discolouration that can occur, or against their ability to stain undyed test fabrics. Let’s take a closer look at the different ways you can assess colour fastness.
The Colour Fastness Tests
Wash Fastness
A t-shirt can experience hundreds of wash cycles in its lifespan, so it’s important to make sure that your screen prints stay bold and bright for as long as possible. Generally, wash fastness tests are designed to simulate rigorous domestic wash cycles, usually at 40°C (104°F), or for higher performance requirements at 60°C (140°F). There are two components to a wash fastness test: a staining element which measures how much colour transfers to another fabric sample, and a change of shade element which measures how much colours leaves the original print.
Wash fastness test results are graded using a grey scale of 1 to 5, one begin the lowest colour fastness and 5 being the highest. Achieving a grade of 4 and above is ideal, of course, certain applications may demand a higher grade.
Alongside colour grading, it’s also important to examine test samples for any cracks that may occur during the wash cycle and its ability to retain elasticity.
Rub/Crock Fastness
Depending on the usage, printed garments may face surface rubbing over time. The term “crocking” refers to a print’s potential to release colour when rubbed. Naturally, deeper colours can have the tendency to perform worse that lighter colours due to a higher pigment loading.
Crock fastness tests are performed using a sample when it’s both dry and wet, and a shade change grade is applied using a numeric system that mirrors wash fastness (1 being poor, and 5 being excellent).
Generally, a rating of 4 and above demonstrates strong performance for dry-rub fastness, and a rating of 3-4 and above is a positive result for wet rub fastness. This can of course, depend on the requirements that may be set by a customer.
Light Fastness
As the name suggests, light fastness refers to the degree in which fabrics or prints can fade or discolour when exposed to sunlight. This test is performed using apparatus designed to simulate sunlight and exposing a colour sample to the light. The test is measured against a blue wool scale of 1-8 grades, 8 being the highest and 1 being the worst light fastness. You can refer to the technical data of the different light fastness grades of pigments for screen printing inks. Here’s the colour chart of the MagnaPrint® Eco Pigment range.
Colour Fastness Considerations when Screen Printing
When it comes to physically ensuring that screen prints have excellent colour fastness performance properties, what sort of considerations do we need to make on press and in production?
1. Properly Cure Your Prints
It feels like it’s a given, but it’s the most important way to keep colour locked into your screen prints. Always be sure to follow the technical data provided for the MagnaPrint ink system that you’re working with. Some systems may require higher temperatures than others or longer dwell times in the dryer to fully ensure that the print cures to the garment.
2. Don’t Overload Your Pigments
Some ink systems have a lower maximum pigment loading percentage than others. For example, our high solids water-based range, MagnaPrint® AquaFlex V2 has a maximum pigment loading of up to 12%. The MagnaPrint® HB Range on the other hand can be loaded up to 9% with pigments, and discharge products like MagnaPrint® Discharge ULF are even lower, with 6%.
If you keep within these guidelines, you’ll ensure that you aren’t adding too much pigment to your base, and in turn prevent issues with colour fastness on your finished prints.
3. Test the Suitability of Your Fabrics
It isn’t just the ink system and pigments that play a role in colour fastness. The garment or fabric you’re printing on plays a factor in achieving strong performance to the aforementioned tests. It’s always worth test fabrics you aren’t familiar with beforehand to avoided unwanted surprises. This is especially true when printing with discharge inks, as the overall dischargeability of the reactive-dyed cotton plays a role in colour fastness. What’s more, fabrics treated with silicone softening agents or other treatments can reduce the penetration of ink onto the fibre.
4. You Can Use Crosslinkers for High Fastness Requirements
Though MagnaPrint® inks and pigments have been developed across the range to provide high levels of colour fastness, there can be situations where you need that extra boost for even further levels of durability. This is where a crosslinking additive like MagnaPrint® EcoFix XL can be utilised to further improve wash and rub-fastness performance.
Stay Fast
Wash fastness and rub fastness are two of the most important colour durability tests for screen printed textiles, however several other standards such as colour fastness to perspiration, sea water, and dry cleaning are employed throughout the textiles industry where the end use dictates it!
We hope this article provided a useful overview of the topic and how you can achieve the best results in practice. For more technical information check out our Technical Hub.
