Testing for color fastness before sewing clothing is especially important when your item will be washed over and over. Imagine if you made a beautiful red and white spotted dress with a white ruffle and the red ran all over the ruffle after the first wash. Disaster! It would be awful if all your hard work sewing or an expensive item was ruined in the first wash.
How to Test for Color Fastness
Ideally, you should always pre-wash your sewing fabrics. Not just to test for their color fastness but also to pre-shrink.
If pre-washing fabric is not possible, here is how you can still check for colorfastness.
Further Reading - How to Prewash Fabric
Step 1 - Cut Scraps
Cut small pieces of your fabric and sew them onto a piece of white fabric roughly double in size.
Make sure your white fabric is cotton or another natural fiber such as linen. Polyester doesn’t absorb dye so you won’t get accurate results when doing a color fastness test.
Step 2 - Fold the Fabric
Fold the white fabric in half so the colored fabrics are sandwiched in the middle.
Wet the fabrics thoroughly the way you wish to wash your final sewn item. This may be in hot water or cold water and with or without soap. Generally hot water with soap results in the greatest color transfer.
Leave your test color fastness fabric for half an hour still folded up.
Step 3 - Check the Results
Check whether the white fabric has any dye transferred onto it.
You can see from my test that the darker denim and the red run while the chambray and light blue do not. I would not put a white cotton lace on the denim or red since it would probably have some dye transfer.
Color Fastness - Problem Solving
If the colored fabric is running, then you could try washing it in a salt wash to set the dyes better. A small amount of white vinegar can also be tested. Test a small scrap for color fastness before you dunk your whole fabric into either salt or vinegar.
There are also commercial products available to stop dye running.
However, if you still find the color is bleeding even after washing the fabric, you might just be better using it for another project without contrasting colors.
Do you test your fabrics before washing? Comment below.