If you want to paint on denim with acrylic, it's important to first familiarize yourself with some of the characteristics of acrylic paints. One thing to be particularly mindful of is that acrylic is a fast-drying paint and can easily dry out before your project is complete. An advantage to using acrylic on denim is that acrylic lets you build on layers, so you can apply the acrylic with a thin coat or make it heavier by painting more layers.
Preparing the Denim
Washing the denim is the first step in preparing the fabric. You don't want to paint with acrylic on dirty denim because grime or residue that is left in the material will be painted over and could interfere with your masterpiece. Throw the denim into a load of laundry and use a mild detergent. Avoid using any fabric softener; fabric softener will give the denim an oily residue, which will make it more difficult to paint over. After the denim is washed, dry it completely in the dryer. Washing and drying the denim may cause the fabric to slightly shrink, which is beneficial for stretching out the fibers so that the paint doesn't buckle.
Preparing the Paints
Acrylic paint dries fast. Once applied, the acrylic can dry within a few minutes. The paint can also dry out if you empty the paint tubes onto a palette or in an egg carton in advance. Because of this it's important to time the painting project so that you expose the paint to the air just before you are ready to begin. Plan exactly which paints you want to use for the craft so that you aren't drying out paint that you won't use.
Using Fabric Mediums
As acrylic paint begins to dry on the denim -- and as you wear the denim and run it through the laundry -- the paint may become flaky and peel off, which is the nature of denim and other fabrics. To avoid this, mix the acrylic paint with a fabric medium first. A fabric medium, which can be purchased from a craft store, is designed to stay on fabrics like denim and can stand up more effectively to wear and tear than plain paint. The acrylic paint and fabric medium should be mixed according to the directions on the packaging.
When it comes to painting directly onto denim you have some choices about the application process. One idea is to use a stencil and to paint a design that is pre-drawn. Another idea is to freehand the painting onto the fabric. You can freehand the image first with a fabric marker and then go over it with the acrylic paint. The acrylic paint is thick enough to cover the evidence of the fabric marker. Apply the acrylic paint with a natural hair paintbrush, which is effective for producing clean, streak-free strokes.