Color Changing Screen Printing

For Maker Camp we always have a ton of fun creating our camp t-shirts. This year to put a twist on things, I decided to do my tribute to the totally rad ’80s by using color-changing inks for heat and light reactive tees. We also did some fun glow-in-the-dark projects, because everything glow-in-the-dark is fun! The project was so popular with the kids that I modified the activity a bit to bring it to the World Maker Faire 2016 in New York City as a project for the kids.

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What You’ll Need:

All in all, screen printing anything is a pretty simple process. The toughest part if getting your hands on the reactive pigments. I really the like those sold by Solar Dust. They have a wide selection of colors from which to choose — color-changing, glow-in-the-dark, holographic, fluorescent, glitter and much more. Plus their pigments are all non-toxic, and the customer service is amazing. They happily answered all my questions, so I was able to plan my project with confidence. I highly recommend Solar Dust for your projects!

The next big question

Here’s what you need:

  • A substrate (the washed t-shirt, paper notecard, etc. on which you want to print)
  • A translucent or transparent base
    • Note: I used Speedball’s transparent base for fabric shirts and a Liquidtex matte gel for paper. An 8 oz. bottle of base easily did 40 or more shirts. An 8 oz bottle of matte gel with give you hundreds of 4×6″ paper prints. A little goes a long way.
  • Reactive dry pigments
    • Note: As I mentioned above, I like Solar Dust pigments. Plan 2-3 grams of pigment per 4 oz. of base. It is sold in 10g quantities for around $20, which means you’ll be able to make many projects. They also offer a sample pack, with 1g samples of 10 colors.
    • If you are in a pinch for time, Hali Industrial (available on Amazon) does sell thermochromatic pigments as well. I have used this pigment and it works, but because it isn’t gaurenteed non-toxic, like Solar Dust pigments are, I am more hesitant to use it with kids.
  • A prepared silkscreen OR
  • Your own DIY screen, which uses
    • A wooden picture frame (Check craft stores for wooden blanks or the dollar store.)
    • Sheer fabric (I used an old curtain panel. You can also buy your own screen printing silk.)
    • Staple gun
    • Scissors
  • Adhesive-backed Vinyl
  • Knife to cut the stencil, or digital cutter
  • Transfer paper
  • Squeegee (or an old credit card for smaller projects)

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Creating Your Screen:

Unless you purchased prepared screen, as I did when making large projects like t-shirts, you’ll need to start by making your screen.

First wash and dry your fabric, unless you purchased professional silk screen. You don’t want dirt, starch or sizing to block the adhesion of the vinyl later or gum up your inks when printing. You want fabric with a small mesh to it. I also find that synthetic fabrics are generally stiffer and easier to work with when stretching. They are also easier to clean between prints.

Next, remove any glass or backing from the frame. Remove or bend flat the metal tags that typically hold in the backing and picture. Place the frame, front down, on the fabric and cut around it, leaving 1-2 inches (depending on the thickness of your frame) around the outside.

Starting on a long side, fold the fabric over from the front to the back of the frame, straighten and staple. Don’t skimp on the staples, by the way. You want the fabric held tight and strong.

Grasp the fabric on the opposite side, and pull taught, folding it over the back of the frame as well. Starting in the center, staple the fabric to the frame. Keep the fabric held tightly as you staple along the edge. Repeat for the short sides of the frame. This is an important step. Take your time to get the fabric tight and flat.

Pull the corners up, make sure the fabric is tight against the frame and fold down into a triangle shape, then fold against the frame. Staple. The goal here is just to keep the corner fabric tight and flush against the frame. Trim any excess fabric.

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Making the Stencil:

Now it’s time to make our stencil, which masks the areas we don’t want to print. Using adhesive backed-vinyl from the craft store, trace your design onto the front and use a sharp knife to cut it out. Be sure to go just through the vinyl, not all the way through the backing paper. Since we are using transfer paper, you don’t need to worry about all the pieces being connected for this project.

I used a digital cutter, specifically Silhouette’s Cameo to get a precise cut, easily. I also like using the Cameo when I am making several screens that will all be the same. For example, for Maker Faire I had at least 6 screens ready to go at all times. Hand cutting all of them, especially tiny details like lettering, would have taken a lot of time. Using a digital cutter is also great for working with kids, as they can focus on the design, not the fine motor skills, which may still be under development for younger students.

Once the stencil is cut, you may need to “weed” it. This means you remove the parts of the stencil where you want the ink pass through, the parts that will make your printed image. A sharp knife or tweezers help with the process. Discard the weeded vinyl and trim the edges of the your stencil, as needed.

Cut a piece of transfer paper to match the size, or a bit larger, of the stencil. Starting at the top, attach the transfer paper to the front of the stencil, rolling it over the stencil and removing the backing as you go. Be careful not to create bubbles or damage the delicate stencil.

Now remove the backing from the vinyl. Orient the stencil over your frame, and slowly roll it onto the fabric, again starting from the top and being careful to avoid bubbles or stretching. Pro tip: If you are not planning to use your homemade stencil for another design, or if you are planning to do many designs of the same print, apply an added blast of spray adhesive to the back of the vinyl before adhering it to your fabric, to ensure to sticks well. Once the stencil is transferred, carefully remove the transfer paper. This is the most challenging part of the process, in my opinion, especially if your stencil has small details.

Use masking tape to cover any areas left uncovered by the the stencil. Make sure the edges along the frame are well sealed. This masking tape will likely last for hundreds of prints, but always plan to have extra with you when printing. It’s handy.

If you are looking for further details, great instructions for making vinyl stencils for screen printing are available on Make Magazine. That’s how I got started!

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Inking It Up:

Now it’s time to mix up your ink! The suggested starting ratio of dry pigment (color-changing) to clear base is 2 grams to 4 ounces. (If you don’t have a digital scale available, approximately one teaspoon of dry pigment mixed into your base is a good place to start.) Add the pigment, mix it very well, then test a small amount on a scrap of fabric or paper. I’ve found that the UV reactive dyes need a higher ratio of pigment to base, so testing to make sure you have the effect you want is important. Every pigment is a little different.

Once you have the color you want, give the mixture another stir and let it sit overnight. This helps the dye saturate the base, and I’ve found it gives better results, especially when using thick bases, like those for printing on paper.

A quick note about mixing pigments: Some pigments, like photoreactive pigments that change color int he sun, may be available with a color change of clear to color. In other words they are invisible without sunlight. This is a lot of fun for t-shirts that make images magically appear in sunlight, but was challenging for students, because they couldn’t see the print and weren’t sure the image transferred well. I found that adding a bit of florescent pigment helped, so that you had a color-to-color change. You can’t add just any pigment; for example adding acrylic paint or other opaque mixes will block the light needed to cause the reactionThe same trick works for glow-in-the-dark pigments.

And a quick note about your base: It’s very important that your base dry to clear. The clearer the base the better, especially for photochromatic pigments and glow-in-the-dark colors that need the energy of light to work. Also, you want to test your base in small quantities before trying a big run. It needs to be thick enough put on the screen without running. If it’s too thin, it’ll go right under the stencil, making a mess. Also, you don’t want anything that dries too quickly, as it’ll dry in your screen, potentially destroying it. This is one reason I don’t use straight acrylic paints. They dry much too quickly.

Time to start printing! Place your material under the screen. To keep it in place, you may want to use a bit of masking tape to hold it in place. With shirts, I use a bit of spray adhesive on a wooden board and place the shirt over the board, so that it stays put and the ink doesn’t bleed though to the back of the shirt.

Then simply scoop some of your ink onto the screen edge, creating a line of ink, and use a squeegee (or for small projects, an old credit card) to drag it across the image. I do two passes — the first to “flood” the image and fill the tiny holes in the fabric with paint, and then second with pressure to push the ink through the fabric onto the paper or shirt. Aim for a consistent single pull of ink across fabric.

It may take you more than one pass as you learn, but that’s ok. Just be careful not to go too far, as the paint can run under the edges of the stencil if you take too many passes, blurring the image. Also pull the ink in one direction when possible, to avoid damaging or stretching the screen or stencil. Since this is a vinyl stencil, pull the ink across the stencil in a direction that won’t lift tiny details (like the points of the “M” in my image).

Another quick pro tip, keep a basin or try lined with damp paper towels handy. This will keep your screen moist when not in use. You do not want to accidentally allow the ink to dry on the screen! That’s create unwanted masks and block the screen.

Lift the screen, and you’ve made a color changing print! Let it air dry or use a blow dryer to set the ink. If printing onto fabric, be sure to heat seat the shirt, turned inside-out, in a hot dryer for 30 minutes. In general, be careful not to expose the inks to heats over 200 degrees F, as that can degrade the ink and cause the color-change to stop happening. The color change should last a amazing 5,00 sycles before it finally gives out, so you’ll have lots of opportunity to play.

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From there it’s time to add googly eyes, “jewels”, puffy paint or marker drawings to make the design your. Go crazy!

About the Science:

Want to learn a bit more about the science of this project? Great!

Screen Printing:
Screen printing, or silk-screening, is a printmaking process where ink is pushed through a mesh onto fabric, paper or another surface. The ink is blocked in some areas by a stencil, creating a single color image.
Most professionals create the stencil using a black and white image which is burned into a chemical emulsion and hardened by light onto the screen. Here we used self-stick vinyl, digitally cut to create our stencil.
Screens are reusable for many prints. To create a multi-color image, several screens are used. There are a variety of inks available for screen printing, but we made our own using special color-changing pigments.

Color -changing inks:
Our color-changing notecards use thermo- and photo-chromatic pigments in a transparent base for screen printing. The thermochromatic ink changes color when the temperature gets above 86F. The photochromatic ink changes color when exposed to UV light from the sun (or a blacklight).

In both cases this is because a chromophore — the part of the chemical molecule in pigment responsible for color. The chromophore absorbs light at a specific frequency; the light that isn’t absorbed bounces off the pigment and imparts color to a molecule. In the case of color-changing ink, the chromophore is reactive to a change in energy, either heat or light. The energy causes a physical change in the chromophore, which changes the way it absorbs light. The reaction won’t go on forever; eventually the pigment will lose its color changing ability, but it will take a long time.

Our glow in dark ink uses a photoluminescent pigment. They contain phosphors – a type of chemical that absorbs energy and re-emits it as visible light. The more light you expose the beads to, the more energy they will have to glow. Different phosphors emit different wavelengths of light, which we see as different colors.

So there you have it! I hope you enjoy making your own color-changing or glow-in-the-dark prints at home!

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