Does the Tide or Persil have optical brighteners?

Not sure...I use Persil ProClean or Tide 3 in 1. Sometimes I use Persil powder.

Same here with my white sheets. What I do is every so many washes, I do a quick wash with Oxi added to the sheets, and then rewash with LeBlanc.

All of my sheets are white, so it does make a difference! I know there are a lot of LeBlanc users on this site so interested in how everyone manages laundering their fine linens.

Wondering if you've tried any other methods to get the sheets whiter? I recently ran my fine white sheets in a 120F soak with just Oxiclean for about 3 hours, then rewashed in LeBlanc. They're actually not super white even from the long soak, I was surprised. I'm thinking of washing them in Miele Ultrawhite powder to get them back to bright white, but thought the detergent might be too harsh and unnecessary for the fabric. The sateen fabric is so soft now from the LeBlanc I'm hesitant to use other detergents.