True burn marks could be caused by several things:
- The temperature is too high on the heat press. Verify the correct temperature is being used for the application. Also verify that the heat press temperature indicator is showing the true temperature of the heat press. Purchase a digital pyrometer from a sublimation dealer to take readings. Do not use a temperature gun bought from a hardware store. Contact the heat press manufacturer for instructions on how to recalibrate the temperature indicator.
- The heat was applied too long. Verify the correct time setting for the application and do not exceed it.
- The heat press platen is dirty. What looks like a burn mark could be contamination on the upper heat press platen. Most sublimation dealers sell products for cleaning the platen.
- The substrate is defective. This is most common with apparel. Sometimes additives have been used in the manufacture of the garment, which may have an effect on the sublimation. An example is neon fabrics. Brighteners (chemicals) are added to neon dyes to enhance the color. They are easily affected by heat. Typically, at around 300 F the fabric starts to turn a brownish color, which looks like a burn, though it’s just a discoloration. There is no fix other than trying a different brand of garment.
—Jimmy Lamb, Sawgrass