I ask you, the smartest people I know.

[butterflydreaming]

Salt is used to set dye (a mordant) in a fabric, such as when tea dying muslin. Salt is also one of the #1 suggested methods for removing a fresh blood stain from fabric.

This is breaking my brain. Why?

My guess is that dyes are not protein-based. Does that sound right?

Comments

[chaoselemental.livejournal.com]

I suspect it is similar in action to soda ash (sodium carbonate). Soda ash is also used both as a fixative for setting dye and as a laundry booster (or used'ta be, hence its other common name, washing soda). So sayeth Wikipedia:

"In domestic use, it is used as a water softener during laundry. It competes with the ions magnesium and calcium in hard water and prevents them from bonding with the detergent being used. Without using washing soda, additional detergent is needed to soak up the magnesium and calcium ions. Called Washing Soda, Soda crystals or Sal Soda in the detergent section of stores, it effectively removes oil, grease, and alcohol stains. Sodium carbonate is also used as a descaling agent in boilers such as found in coffee pots, espresso machines, etc.

"In dyeing with fiber-reactive dyes, sodium carbonate (often under a name such as soda ash fixative or soda ash activator) is used to ensure proper chemical bonding of the dye with the fibers, typically before dyeing (for tie dyes), mixed with the dye (for dye painting), or after dyeing (for immersion dyeing)."

As for why...? Um, ya got me, but since it works for other oily/greasy stains, I'd bet that protein-based vs non-protein-based is a good guess.