Polyester doesn't absorb standard Rit dye well, so use the company's Rit DyeMore product to successfully change the color of your polyester fabric. The synthetic material requires constant heat to take the dye properly, and the stove-top method of simmering it with the dye works best.
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Getting Ready to Dye
Figure out how much dye to use by estimating how much the polyester fabric weighs. Food or mail scales work well for this, giving you the amount in ounces, but use your best guess if you don't have the right kind of scale. For example, a lightweight ladies' shirt might weigh 4 ounces. When you want the basic dye color as the finished product, use Rit DyeMore in the ratio of one bottle per 2 pounds of dry polyester fabric. So if you're dying a 4-ounce shirt, you need about 1/8 of a bottle of Rit DyeMore.
Use more dye to achieve darker colors. Start by doubling the recommended amount, and add more as necessary.
Wash the fabric in warm water, using laundry detergent to remove any finishes coating the polyester. There's no need to dry the item; it works best if it's damp when you add it to the dye mixture.
The fabric needs room to move around and be fully covered by the water, which means you need a pot large enough to hold 3 gallons of water and the polyester item, with some room left over so it doesn't overflow when you stir. Heat the water until it's almost boiling, ideally 180 degrees Fahrenheit or when bubbles start forming along the sides. Pour in the desired amount of dye and 1 teaspoon of dish-washing liquid, and then stir to combine. Test the color with a strip of paper towel, and add more water to lighten the color or more dye for darker colors if necessary.
Use metal utensils to ensure they don't absorb the dye, which can discolor wood or plastic. Tongs help you grab and turn the fabric in the water for even coverage.
Place the fabric in the simmering water, keeping it in constant motion by stirring so the dye penetrates all areas evenly. After 30 minutes -- or longer for a deeper color -- remove the fabric and rinse it under warm water, slowly decreasing the water temperature until the water runs clear. Hand wash the item in warm water and laundry detergent to help remove any excess dye. Air-drying the fabric helps the dye set properly.
The dyed color looks darker when the fabric is wet. If it looks like the perfect color while simmering, leave it in for a few more minutes to make sure the finished dry color meets your needs.
Use gloves and an apron to protect your hands and clothes from the dye. Any accidental contact can create discolored areas.
Rit DyeMore works with natural fibers such as cotton, as well as many synthetics including polyester. When you dye a polyester fabric that's a blend with a natural fiber, the shade might be slightly darker than when you dye 100 percent polyester because the cotton absorbs the dye easier. If a section of the item, such as a lace design on the back of a dress, is 100 percent cotton while the rest of the garment is 100 percent polyester, the cotton section is likely to be darker than the polyester section.
Regular Rit dye works on natural-fiber blends that are no more than 40 percent polyester, although the color turns out lighter than on 100 percent natural fabrics.