Years ago, I monkeyed with tea-dying fabrics — with varying results. At first, I couldn't figure out what the attraction was to taking a nice, white piece of muslin and turning it, well, dingy brown. Then I learned how to get a little more creative.
Two things changed my outcomes: using a resist to make patterns, and using different liquids.
The resist: Dye the fabric, but beforehand apply a compound in words or patterns that will block the dye, leaving the pattern in the fabric's original color. Some instructions suggest using Elmer's glue; it's often not as easy to remove in the end as is suggested. I've used wax before — I used some beeswax I had on hand in a work bench, but you can buy wax sticks for this purpose, seen here. Crayons work, too, and look here for a nifty technique using bleach to white-out patterns.
As to the other liquids, nearly all tea-dying instructions you'll find discuss the practice in terms of black tea. (And use something inexpensive, of course. Don't waste your fine keemun on the drapes!) I suspect, however, that green tea would provide interesting, if subtle, results, too. I also suspect — having had the misfortune of spilling some on a carpet once — that strong herbals such as hibiscus would also work well. The trick: play around with different dyes on the same fabric. One project I enjoyed a while back: I dyed a set of white napkins with tea, but then I dyed their edges (an inch or two, by suspending them into the liquid with clothespins) with coffee, so there was a nice tea tint to the whole napkin plus ribbons of darker brown at the edges.
5 years ago