When buying fabric you may occasionally come across the term Prepared for Dyeing or PFD. This means that no starches, sizing or finishes have been used on the fabric. These treatments, including optical whiteners, will interfere with the absorption and therefore the effectiveness of dye.
Although your fabric has been sold as 'dressing free' it should still be prepared for dyeing because it will have attracted grease or dirt during handling.
Another problem to be aware of is residue from deodorants and body lotions. You may have bought a 100% cotton t-shirt but if you tried it on in the shop, there is a good chance that some of these substances will have transferred to the fabric.
Fibres and yarns will have been 'contaminated' in a similar way to fabric. Wool fibres may still retain some of the lanolin (a waxy substance secreted by the sebaceous glands of the sheep).
Any residue on material will potentially act as a resist to repel dyes, paints and printing inks.
We recommend that all materials are rinsed out in a solution of Synthrapol which is a non-ionic detergent and does not leave the alkaline residue usually left by household detergents.
Use 5ml of Synthrapol to 2-3 litres of water for each 100g of material and stir gently over a 15 minute period (take extra care not to over agitate wool as this will felt the fibre). Rinse thoroughly in warm water and your fabric, fibres or yarns are now Prepared for Dyeing.