1. After your event leave as much color on your shirt as they can. We know you'll be tempted to shake it off.
2. Lay your shirt on a flat surface, preferably outdoors, on a piece of cardboard.
3. Spray your shirt generously with a mixture of vinegar and water on both sides. Some people like to spray their shirt multiple times over a couple of days.
3. Let the shirt dry completely.
4. Place an old cloth (something you wouldn't mind being stained) between the shirt and your iron.
5. Iron both sides of the shirt.
6. Then just wash as normal. This is similar to how tie-dyed shirts keep their color.
Here's another cool idea that came from a customer that you guys might want to try. This was from a birthday party. They taped stencil cutouts on their shirts, then sprayed adhesive spray on them before they threw the powder at each other. When they washed the shirts, the color stayed on the shirt everywhere the adhesive was sprayed.
Until we heard this, we only knew about the vinegar/water mixture. We tried the adhesive spray method out this past weekend and it worked great. The only thing I would want to remember next time is that only the first color that hits the adhesive on the shirt sticks. I threw a handful of pink on my design and then blue, green, etc. I should have been a little less generous and sprinkled several colors on the design. Only pink stuck to the shirt.
We have the best customers in the world! So creative!