There is a whole (mostly boring) science of detergency (how detergents work). Every detergent has a specific concentration at which detergency takes place. You can find this out from Material Safety Data Sheets and/or other product information from the manufacturer. Let us say, as an example, that Detergent X achieves detergency at 1%. Below 1%, you form a chemical scum, and you don't get any cleaning action. Too far above 1% and you will have to rinse until the cows come home to get it out. The trick comes in the calculation of how much detergent you need in relationship to the size of your wash bath. And, if you have pre-wet the rug (as you should), you also have to estimate the quantity of water in the rug before you add the detergent solution.

I'm not sure I like the analogy of a detergent residue as a "clear dye." The analogy of a hair conditioner is probably more apt. There has been some research done on the presence of residues after cleaning using appropriate concentrations of detergent and thorough rinsing, but to date, no ill effects of the residues have been shown. We have examples of pieces cleaned with ORVUS over quite a number of years, again with no evidence of a problem.

As for other detergents. Some conservators like Triton-X (good for some kinds of dirt and not for others). It is important to use a detergent and not a soap. Soaps form a scum when they come into contact with acids (a likely byproduct of deterioration in textiles), and make a general mess. The highest-quality detergents are shampoos (not the "no tears" formulae that are pH balanced for eyes rather than hair), but it's almost impossible to find a true detergent shampoo without dyes, perfumes, and other additives that might not be appropriate for cleaning a rug.

thank you for the information.

Perhaps you might comment of the cleaning of embroidries with silk or wool thread . . .
on cotton
on linen
on wool
on silk

Sincerely

Richard Farber