MsEithne

No, they are not the same substance and they are not interchangeable.

Retayne is composed of molecules with a positive charge. These molecules are attracted to the negatively charged dye molecules. When the two molecules stick together, it makes them larger, so that they stick between the fibres of the fabric more effectively (think Winnie the Pooh).

Retayne is applied using hot (over 140 degree F) water. Once you have treated fabric with Retayne, washing the fabric in hot water will wash out the Retayne.

According to Paula Burch, Retayne has two main drawbacks: a) it contains a small amount of formaldehyde and b) there is growing evidence that fabrics treated with Retayne are less lightfast. In effect, it is possible that what you gain in washfastness, you lose in lightfastness.

Everything in life is a trade-off and there is never a single answer that is right for every person in every single situation.

Synthrapol is a neutral detergent which contains no optical brighteners. The neutral pH means it is good for protein fibres (which prefer acid environments) and will not create a wash environment alkaline enough to affect fabric dyed with fibre reactive dyes. For a long time, Synthrapol was believed to be somehow better at suspending loose dye particles in solution, rather than letting them settle back down onto the fabric but this has been largely disproven (even though there are still advertising claims to that effect).

Synthrapol does not have any optical brighteners in it, which are special dyes that convert UV light to make light colours appear lighter. Manufacturers include them in most detergent formulations because they make the detergent seem more effect at getting light coloured items cleaner (we've been carefully taught via advertising that whiter equals cleaner).

Optical brighteners also make dark colours appear lighter or washed out, so a quilt that relies on the richness of dark colours for its impact may appear less dramatic.