Remove the canvas from the umbrella frame. Wash the canvas in the washing machine without adding fabric softener.
Put the soda ash and one gallon water in a plastic bucket and soak the canvas in it for about 15 minutes. Remove the fabric and wring out all the water. Throw away the liquid in the bucket and rinse the bucket.
Put the dye powder, urea and pickling salt into the large plastic Ziploc bag. Add water to the bag and mix well. Make sure you are wearing gloves and a dust mask before mixing.
Place the umbrella canvas into the resealable plastic bag. Zip the bag and move the canvas around till the dye covers the fabric completely.
Leave the umbrella canvas in the bag for one day to cure in the dye.
Fill the two buckets with plain water.
Remove the umbrella canvas from the dye mixture while wearing gloves. Put in one bucket of water, rinse and wring out the umbrella canvas. Put the umbrella canvas in the other bucket of water and rinse. Repeat the rinsing twice until the water runs clear. Finally, wash the canvas with mild dish soap and leave it to dry.