Recently I posted about the difference between canvas and muslin, and in that post, I mentioned painters backdrops and promised a future post on the subject.
There can be confusion as to whether to choose flame retardant or non-flame retardant heavy weight theatrical muslin for a painters backdrop. The fact is, when paint is added to the surface of a flame retardant fabric, the fabric becomes non-flame retardant. Therefore, steps must be taking to make a painted backdrop flame retardant.
First, prior to painting, a special flame retardant additive should be added to the paint. A FR paint additive will not change the color or opacity of the paint, and it will help ensure that the face of the theatrical backdrop is flame retardant. Second, after the face of the backdrop is painted and the paint has dried, the back of the backdrop should be sprayed with a topical flame retardant chemical designed for natural fibers.
Since painting a backdrop nullifies the flame retardancy, you would think that you should always choose a non-flame retardant muslin for a painters backdrop. Non-flame retardant muslin is more affordable than flame retardant muslin, so why spend the extra money for flame retardant muslin when you will have to retreat it anyway?
The reason to consider utilizing flame retardant muslin for a painters backdrop is related to the issue of shrinkage. As theatrical muslin is composed of cotton fibers, it is prone to shrinkage. When a water-based flame retardant is applied at the mill, the fabric then becomes “sized” (pre-shrunken). Therefore, once the FR muslin is sewn into a backdrop at the desired finished size (height and width), and then paint and additional flame retardant is applied to the surface, there is very little (or no) additional shrinkage of the material. The painted backdrop will end up at approximately the same size as the sewn but unpainted backdrop.
For experienced scenic painters who plan to utilize a paint frame, a non flame retardant muslin works fine. The tension of the paint frame helps prevent shrinkage. For less experienced scenic painters and/or those who will not be using a paint frame, we recommend purchasing a painters backdrop manufactured using flame retardant muslin. This way, shrinkage will not be a significant concern.