How do I restore the sheen to my silk pillowcases?

I’ve just taken delivery of an early birthday present (hey, the delivery date was possibly next month) of a silk duvet cover. It was immediately noticeable that the sheen on my 18 month old silk pillowcases was severely lacking. A quick Google suggested that a dilute vinegar rinse was required. But that hasn’t actually helped (and I washed the pillowcase beforehand). So, what do I need to do?

Bump?

How did you wash them? I don’t think silk is ever supposed to be washed in anything but cold water and very gently.

Silk being a natural fibre, it’s gonna wear and get softer with age. I don’t think you can restore it back to it’s newness and shine. I have one real silk blouse I threw in the wash with some other delicates and used Woolite, it came out looking a bit bedraggled. I took it to the cleaners and they recleaned and ironed it somehow. It still looks different than it did new but I like it anyway.
I have an old crazy quilt with silk and velvet patches and lots of silk ribbon embroidery. I have never washed it. It had obviously been washed in the past and all the silk is un-shiny and slightly wrinkled. It looks good to me. Vintage, I guessed you’d say.
All that, to say I don’t see how vinegar could refurbish your cases.

I see Google advice says the vinegar will work. I don’t think it will hurt them, I would try it.

ChemBrite Silk Luster

As noted in my OP, I tried a vinegar rinse and it din’t work.

Silk is not naturally shiny white. It is given artificial treatment to make it appear as if it is, and I’m guessing that has deteriorated somehow.