One of the toughest things to do in screen printing is to print vibrant light colors on dark shirts while maintaining the soft fabric feel we all love. There are two main types of ink used in textile printing, and they both have unique advantages and deficiencies. Plastisol ink adheres to the apparel by chemically bonding with the top of the fabric. It offers extremely opaque and vibrant colors but significantly takes away from the softness of the apparel wherever it is printed. Alternatively, there is what’s known as water-based ink. This ink actually blends into the fabric. This ink does not affect the softness of the fabric. The downside, however, is that the ink is not very opaque and therefore does not show up well when you print on dark shirts. As dire as this situation sounds, fear not! There are some solutions.
What’s a screen printer to do? As in most situations, the answer is “mix additives into the ink.” There are an astounding number of additives out there. Some make the ink stretchy, others help the ink dry faster, some even expand vertically to give your ink a three-dimensional feel, or allow you to print on metal. By now, you may have guessed that there are additives which address the two problems brought up in the introduction: lack of softness (plastisol) and lack of vibrancy (water-based). For plastisol inks there is an additive that softens the ink and decreases the hand, or textured lift, off the shirt. The solution to the problem of water-based ink is a little more complex.
Why did I choose to focus this entry on discharge ink, the solution for using water-based ink on dark materials? For all I know, using softened plastisol could be a superior solution than discharge water-based ink (keep your eyes peeled for a post comparing the results of both solutions). But there is a certain fascination with discharge that comes from my understanding of how the process works. Let me take a shot at explaining it to you.
First you calculate (or, guess) how much white ink you’re going to need to print the 100 panda bears on black shirts for the 100 shirts you’ve been commissioned to make. Then you multiply by 1.5, just to be safe. One of the downsides of most additives is that the shelf life of the ink is greatly reduced and you can’t mix the leftovers back in with your main ink supply. Once you have your ink in a separate container, you mix in the additive and get ready to print. What the discharge additive does is combine a t-shirt-dye-removing process with the ink color application. It removes whatever dye color is in the areas it is applied (black, in this case) and simultaneously applies a new color (white, in this case). That’s the theory, at least. Discharge ink is notorious for being unpredictable, so you have to test a lot of different shirt brands and colors before doing your final print. So, after all your meticulous planning you lift up the screen after your very first print to see how it came out…And that’s what screen printing is all about!