Transfer paper will become yellow due to incorrect application during the ironing stage. Users often place a great deal of attention selecting the correct paper (dark vs. light, inkjet vs. laser etc) and even more attention around the desired design, but it is the ironing stage together with incorrect heating settings which on occasion can fail the entire project.
When the transfer sheet becomes yellow it has effectively been burned. The sheet contains an upper layer that under heat will melt onto the fabric, thereby transferring the design from the sheet onto the fabric. Therefore enough heat is essential to release the design and get it to melt into the fabric, but too much can burn this layer causing it to appear yellow or other forms of discolouration.
Common incorrect heating settings from most popular to least:
Ironing in one place – During the ironing stage, it is curial to work in small circular motions and to cover the entire design. Ironing one area motionless can lead to this area overheating and that particular place yellowing.
Ironing for too long – It is important to adhere to the required time. Ironing even in a circular motion can burn the transfer if you spend too long doing it. Note that the recommended time assumes that your transfer is of an A5 or A4 size, therefore if transferring smaller design such as a logo, you will need to cut the required time accordingly.
Too much heat – The recommended time to iron is derived from the recommended iron output measured in watts. Instructions are based on a 1400w to 1800w iron. If your iron exceeds this, you will need to adjust the correct time, ensuring not to meet or exceed the duration which is based on 1400w to 1800w output iron. Naturally, an 1800w iron on maximum heat setting will provide more heat than the 1400w one, so adjust time accordingly.
If the ironing was too short due to being over cautious and it looks like an upper sticker on the shirt rather than a transfer, you can always put a silicon paper on top and iron it again so it melts better into the fabric.
Once the transfer has yellowed, there is no way to rectify it. You will need to obtain further transfer papers and repeat the process, this time ensuring that you pay attention to the correct heating settings. Transfer paper becoming yellow is uncommon and can quickly be resolved by ensuring the correct settings have been applied.
Durability of the transfer is achieved by effectively getting the upper layer to melt deep into the fabric and it can only be done using heat, pressure and time. Equally, under heating the transfer may also cause problems down the line. Most notably resulting in a weak transfer that will see the design easily rub off when it comes in contact with other materials or removed after the first wash.
Remember, the entire area of the transfer needs the same heat, time and pressure so make sure you cover the whole sheet giving attention to the corners that get neglected in many cases.