How do you wash cotton silk?

Cotton silk is quite strong and durable when dry but a bit more fragile when wet. It is much stronger either wet or dry than a pure silk and is much easier to clean and care for. It is best to hand wash in warm water using a liquid detergent made for delicate fibers, rinse in very cold water and hang to dry. Do not wring out or twist the wet fabric. Instead gently squeeze out excess water and then soak up more excess water between to thick and thristy towels. It can be ironed using the silk/low setting on your iron. Press on the wrong/underside of the garment and Use a press cloth. A press cloth is a layer of plain cotton fabric placed between the dress fabric and the sole of the iron. It prevents scorching and damage. Or if you have a steamer use that. The steam setting on your iron will also work. Again, cotton silk can handle the heat or the iron better than a pure delicate silk.

Some people machine wash cotton silk of the hand wash or very delicate cycle. Not all machines have a hand wash cycle and use just the regular delicate cycle. Some will wash and dry by machine using the delicate or low setting on the dryer. I personally would hang to dry and and press as above.

Some people won't take any chances and will dry clean cotton silk. If you can afford dry cleaning then that's a good way to care for it. If you can't then you can hand wash it.

Here's some very helpful advise from the Martha Stewart website: http://www.marthastewart.com/270610/how-to-wash-drycleanable-clothes and about cotton silk here: https://sewing.patternreview.com/SewingDiscussions/topic/69657

Which is it, cotton or silk? Be clear.

Look on the tag to determine exactly what the material is. And while you're reading the tag for that, flip it over and look at the manufacturer's recommendations for how to care for the garment.

I have been sewing for 50 years ans have never heard of cotton silk I think that is mixed up.

"cotton silk"? There's no such thing. It's cotton or it's silk.

Use only a delicate cycle and cold water. Place the garment in a mesh bag to prevent damage from other garments. Wash the silk with similar colors to prevent dye bleeding and use a neutral-pH soap. If soaking is required to remove stains, soak only for 30 minutes or less.

Dry clean them.