Preheat your iron on the highest setting.
Cut a piece of freezer paper large enough to comfortably fit your design. Turn the shirt inside out and place the freezer paper shiny-side down on the shirt’s (inside) front side. Iron the freezer paper onto the shirt. Turn the shirt right-side out. The freezer paper will give structure to the fabric, and prevent the bleach from seeping through to the other side. If the freezer paper separates from the shirt, go over it with the iron again. No need to turn the shirt inside out again.
Draw a design on the shirt with the chalk or transfer the template by tracing the design with a transfer pencil and ironing the design onto the fabric. (See the instructions on the transfer pencil packaging.) A ruler can come in handy for measuring and drawing the lines if you decide to draw freehand.
Prepare a mixture of hydrogen peroxide and water in the ratio of 1:10 (for example, 2 cups of hydrogen peroxide mixed into 20 cups of water) in a plastic container big enough to hold the shirt. The mixture should be a few inches deep in the container. If you prefer, you can fill a spray bottle with 1 part hydrogen peroxide and 5 parts water. Warning: Please use caution when working with bleach products or hydrogen peroxide. Work in a well-ventilated area, and consider using plastic gloves, as hydrogen peroxide is a skin irritant.
Grab paper towel and the bleach pen. Before you take the cap off, shake the pen a few times to make sure you get as much of the bleach gel to the tip as possible. You should repeat this each time after your draw a few lines to make sure you get an even flow to draw with. I always squeeze the pen a bit over the paper towel before I begin, to wipe away any air bubbles and to make sure I get a good flow going. I also do this each time I lift up the pen from the fabric. So keep the paper towel close by!
Start tracing your chalk design with the bleach pen while gently squeezing it. Touch the tip of the bleach pen to the fabric very lightly and try to move at an even pace.
When you’re done tracing your design, wait a few minutes for the bleach gel to start discharging color. You can always lift up the shirt a bit to see the inside and peel away the freezer paper to see how the color is developing and to monitor how fast the gel is spreading.
Hydrogen peroxide stops the bleach action, so when you’re done, gently put your shirt into the container with the hydrogen peroxide and water without removing the freezer paper (see photo). Do not fold or crumple the shirt; you want to keep the design as flat as possible so the bleach gel doesn't rub off onto unintended parts of the fabric. Slowly submerge the shirt into the solution and wait about 10 minutes. Gently rub off any remaining bleach gel from the shirt with your hand, remove the freezer paper from the inside of the shirt, and take the shirt to the sink to rinse it out. If you’re using the spray-bottle method, spray your design with the peroxide and water mix, making sure the bleach design is well soaked. Wait 10 minutes, and then rinse the shirt, washing away any remnants of the bleach gel. Wash the tee as you normally would.
This how-to is excerpted with permission from <a href="http://amzn.to/1EfatIN">"Make Your Mark: Creative Ideas Using Markers, Paint Pens, Bleach Pens & More"</a> from Lark Books.