Unitard Dyes and Paints

Heat Setting Fabric Paints - Does it make a difference?


So here we have nylon/spandex blend in white. The brown paint is Setasilk. Black hatching is Dylon fabric paint. The silk paint is applied with a sponge, the heavier areas are where the paint saturated the fabric. finer detail was not saturated. The black hatching is from a fine-tipped bottle.

Samples 2 and 3 were washed in a gentle detergent (hand soap) in hand-warm water, rinsed in cold water. This is as you would wash a costume after wear. NEVER USE BLEACH ON SPANDEX. (oh hey, I’ll show you why later)


 * 1) the unwashed control sample.
 * 2) paint dried but not heat set.  Both brown and black notably faded, and the unpainted white is discoloured.
 * 3) heat set with a hot iron, high steam, with a linen cloth between the spandex and the iron.

In conclusion - even with heat setting, the paint does fade when washed. However I’d estimate it fades twice as much when not heat set. Heat setting will double the longevity of the paintwork.



Experiment 2 - bleach on spandex.

Sample 4 was soaked in a weak solution of bleach for 10 minutes, then rinsed thoroughly in cold water. While the bleach treatment has reduced the intensity of the paint, it has also notably stretched out the fabric even in this small sample. Bleach destroys the spandex fibres which are blended with the nylon fibres, it is the spandex which is elastic and controls the stretch of the fabric. With damaged spandex, the nylon fibres relax and will eventually stretch out to the fabric’s maximum give. There is no real way to repair this damage.

Acid Dyes on Nylon/Spandex
While this is specifically looking at Cats costumes, it reaches out to a much broader costuming/cosplay application. The authentic Cats unitards used in replica productions of Cats are painted with a thickened form of acid dye, then the dye is activated in a commercial steamer, as is used for silk painting. The acid dyes soak into the very fibres of the nylon fabric, altering the colour, and this creates rich, vivid, permanent effects. Acid dyes generally come in powder form, and are designed to be dissolved in a vat of water, with the fabric to be dyed submerged and simmered, the heat speeding the chemical process. Getting these vivid colours on Nylon/spandex is simple enough for a solid colour, and not too difficult for tie dye/dip dye. But to control the dyes into specific patterns is much harder.

There are a bunch of problems for domestic costume makers trying to replicate this technique. Firstly, thickening the dye solution to make it behave as paint, to control the application exactly. There are some artistic/craft thickeners available commercially, but will they interfere with the bonding of the dye to the fabric? Or the lower tech option, would kitchen ingredients like Agar, or even cornstarch, work?

Also, the steaming process to set the dyes is complex - the fabric must be suspended and surrounded by steam, to allow the heat to penetrate the fibres without any contact between layers of fabric which would allow the dye to transfer. This is based on silk painting techniques. And added to this complexity is the fact that Cats unitards are built on a single seam pattern. If painted before being sewn up, the sheet of fabric is approx 1.5m x 1.5m and a stretch fabric, pulling under its own weight. This requires a customised steamer, to heat the water, contain the steam, suspend the fabric, and to run the process for long enough to set the dyes.

So I have been experimenting with applying acid dyes cold, to nylon/spandex, and using a domestic iron to set the dye. To heat set with a domestic iron, I use a steam iron on its hottest setting, set to produce the maximum amount of steam, and use a light linen cloth (tea towel) to cover the fabric. A hot iron is generally hot enough to melt nylon, and will burn through the fabric if the metal plate touches the fabric.



I made a strong solution of “dark brown” dye with boiling water. This first sample shows spots where I had not sufficiently blended the dye. samples 1, 3 and 4 are consistent in colour. The heat setting did not alter the shade of the dye, but did fix it thoroughly in the fabric. 2 however, clearly lost a lot of the pigment. Before washing out, the dye left a stiffer feel to the fabric.
 * 1) the dye painted onto the fabric.
 * 2) the dye, dried fully, then washed clear.
 * 3) the dye was first heat set, then washed.
 * 4) the dye was heat set, but unwashed.



Using the same dye as before, I stippled the dye onto the fabric. It handled exactly like silk paint, spreading where the fabric was saturated, but remaining discrete when applied lighter. The dye did appear much darker when wet, and dried several shades paler, which is not as much of an issue with silk paints.

The same results as before, only the effects of not heat setting are far more pronounced. The red elements of the dye were not fixed by air drying alone, and when the sample was washed, the red pigments spread throughout the fabric despite it being rinsed under running water. The grey pigments ran and blurred. However after heat setting, the pattern remained exactly as before.



Sample 3 - shows the amount of dye “creeping” up from the fabric scrap being submerged in the bowl of dye. This sample was submerged in the strong solution of dye at ambient temperature. Again, showing the difference between the heat set, and simply rinsed dyes.



Sample 4 - This was the same fabric, treated in the conventional manner - the rest of the dye left over from the painting experiment was put in a pan with several pints of water, and the sample was simmered for 10 minutes. This demonstrates two things - the intensity of colour achieved by submersion is several degrees of magnitude brighter than the painted fabric. And also, this is the result when your submerged fabric is NOT stirred constantly while it is simmering!

So - in conclusion, you can get a decent, light base from sponging acid dyes onto spandex and heat-setting with a domestic iron. However the effects achieved are not significantly different to those from silk paints, possibly harder wearing and longer lasting. Using a painting application and a domestic iron does not give results anywhere near as intense as submersing and simmering the fabric.