Just a few minutes into the activity (and after my initial learning curve), the children made this an almost entirely autonomous process. I only needed to help them rubber band the cups to the tees. They did a great job, even with eight or so at the table, of negotiating the use of markers and taking turns with the rubbing alcohol dropper (of which there was only one). From youngest (young two year old) to the oldest were totally engaged.
Four easy steps
First, we used a rubber band to secure the t-shirt (a single layer or both layers) over a plastic paint cup or glass ball jar.
Next, the children decorated the resulting circle with permanent markers.
Then they used a small dropper to place a small amount of rubbing alcohol in the center of the circle. Some designs needed more alcohol than others to effectively diffuse the color. It takes a few minutes for the diffusing process to complete (great for practicing patience and observation skills).
The final step is to just hang them up to dry and to let the final bits of color diffuse. They dried pretty quickly so the children could wear them shortly afterward.
As for laundering, Rachel suggests heat setting it (wash alone in extra hot water) to get the initial fading/bleeding out and to set.
Next time, we'll try this alternative coloring process from Frugal Family Fun blog.