Dye is translucent, so it only adds to the color that is already there. If you want the dye to appear like it does on the packaging, you need to start with a white base. If you prefer a muted shade, however, you could start with gray linen instead.  You can try dyeing a cotton-linen or rayon-linen blend, but be aware that the results may not be consistent or even. If you are working with yarn, wind the yarn around your hand and elbow to create a large hank. Loosely tie pieces of string around the hank to secure it. Use a funnel to fill a large jug with 1 cup (140 g) of soda ash. Add 1 gallon (3.8 L) of water that is around 105 °F (41 °C). Close the jug and shake it to dissolve the soda ash. Open the jug and set it aside so that the water can cool.  Use pure soda ash (sodium carbonate), not baking soda (sodium bicarbonate). You can find it online and in well-stocked craft stores. If you have hard water in your town or city, add some water softener. This will prevent the minerals from affecting the dye. Place your fabric or yarn into a plastic tub. Fill it with enough of the soda ash solution to completely cover the linen. Let the linen soak for at least 20 minutes. Save the rest of the soda ash for later. The soda ash solution can still be hot for this step. Each brand will be a little different, but in most cases, you will have to mix 2 teaspoons of fabric reactive dye powder with 1 cup (240 mL) of water. Mix the dye with a little bit of warm water to form a paste first, then add the rest of the water.  Wear safety googles and rubber of plastic gloves to protect your eyes and skin. Wear a dusk mask approved for fine particles for this step. Powdered fabric reactive dye is dangerous to breathe in. Use less dye for a lighter shade and more dye for a darker shade. You don't have to use an applicator bottle if you won't want to, but many people find it easier to use than just pouring the dye from the container your prepared it in. How much more dye you prepare depends on how much linen you are dyeing; refer to the manufacturer's instructions for more advice. Take the linen out of the soda ash bath, and squeeze out the excess solution. Set the linen down onto a plastic tray or bag, then squirt the dye onto it. You can create an all-over solid color or a splotchy color. You can even use multiple colors to create a tie dye effect.  Keep color mixing in mind. If you put 2 contrasting colors next to each other, they will form brown then they touch. Squeeze the linen after you apply the dye, then apply more dye if needed. If you dyed your linen multiple colors, be careful not to bundle it up. Arrange the linen so that no 2 colors touch or smoosh together. Zip or tie the bag shut, and leave it in a warm place for 12 to 24 hours.  The place should be at least 65 °F (18 °C). The longer you leave the linen in the bag, the brighter and more vibrant the colors will turn out. Don't worry, fiber reactive dyes are non-toxic, so they won't harm the environment or waterways. The soda ash can also unblock clogs in your sink! Keep rinsing until the water runs clear. It would be a good idea to rinse the linen afterwards with Synthrapol, which helps set the dye into the linen better. You need to use Synthrapol with hot water; follow the instructions on the bottle. Make sure that no soda ash remains inn the linen before you start. Squeeze the linen with your hands until you get most of the water out. Spread it out on an old towel in a well-ventilated area away from sunlight. Allow it to air dry completely before using the fabric or yarn. Once the yarn is dry, snip the strings holding the skein together, then roll the skein into a ball.

Summary:
Choose white linen for best results. Dissolve 1 cup (140 g) of soda ash in 1 gallon (3.8 L) of hot water. Soak the linen in the soda ash solution for 20 minutes. Mix your dye according to the manufacturer's instructions. Prepare more dye as needed, then pour it into applicator bottles. Pour the dye onto the linen using the applicator bottles. Put the linen in a plastic bag and leave it someplace warm for 24 hours. Rinse the linen in cold water. Squeeze the excess water from linen and let it dry away from sunlight.