I like to pre-wash my fabric before dyeing as it removes any of the chemicals that the fabric may have on it form the manufacturing process.  Just throw them in the normal wash machine with some detergent, and wash on a normal cycle.  Hang to dry.

Fill a large enamel pot with onion skins, and cover with water until about 3/4 of your pot is full.  I didn't measure in weight how many skins I had, I just filled the pot, and got down to dyeing.  Bring the onion skins to a boil and simmer on low for 1 hour.

In a separate pot, boil some water and add your fabric to this to let it boil for about 5 minutes or so.  This will help  the dye adhere to the fabric better.

Using tongs, carefully add the hot fabric to the dye pot with the onion skins.  Stir well to ensure no air bubbles are trapped under the fabric.  Simmer the dye and fabric for an hour, then turn off heat and allow the fabric to soak in the dye for 1 day.

*You can keep the fabric soaking for longer than 1 day for a deeper richer color...  I found that I loved the color after 24 hours, but assess and allow fabric to soak for longer if desired.

After your fabric has been sitting in the dye for 24 hours, it should have a bright yellow hue. Discard the dye (I did outside in our forest because I didn't want to get pigment in our kitchen sink) so only the fabric remains in the pot.

Under cold running water, rinse out the dye from your fabric.  Continue to rinse until no more pigment comes out from the fabric and the water runs clear over it.

Allow the fabric to air-dry on a drying rack, clothesline, or over a hanger.  It was a beautiful sunny day when I finished dyeing, so on the clothesline they went!

After my fabrics dried I was so happy with the bright yellow color from the onion skins.  These tea towels would make such a perfect hand-made gift - but I am keeping them because they are a little too beautiful to part with.