The molecular weight is important because the lower the molecular weight, the more likely the protein will actually penetrate the skin and hair and act as a humectant in the stratum corneum or cortex. This means it is good for drawing water internally for dry and very dry skin and hair. If you have frizzy hair, drawing water inside might lead to more frizziness, so choose your weight wisely. (This is probably the reason my hair doesn't like silk - it's already frizzy!)
For something like CroSilk 10,000 (from Croda), a low molecular weight silk, you can use between 0.5% to 20% in your creations. For something like hydrolyzed silk proteins or hydrolyzed silk peptides, you can use 0.2% to 3% in your creations. The powdered silk is fantastic for mineral make up applications and gives it a smooth, silky feeling that also conditions your skin, or you can dissolve it in your heat and hold stage and use it that way.
As with the other hydrolyzed proteins, substitute silk for any recipe indicating hydrolyzed proteins. It is water soluble, and should be added during the water phase of your creation so you can heat and hold it. It needs to be well preserved, so use the maximum preservative indicated for your product. And I wouldn't go over 5% - it's expensive, and 2 to 5% is ideal for our creations (I'd choose 2% to 3%).
I use it in my shaving lotion not only for the silky feeling, but the conditioning and humectant-y properties. And I figure you can never go wrong with lots of moisturizers and film formers for such sensitive areas! (I mean my underarms...I don't need to shave my legs. I know, envy me now! All that head hair and very little leg hair? )
Let's take a look at how we can use powdered silk proteins or peptides in a finishing powder. You can add foundation colours to this, but I leave it uncoloured as an oil control, conditioning, and shine product for my oily skin. The silk feels really lovely in this, and it adds the element of a little conditioning for your skin in a powdered product. (I'll be writing more about foundations in June...)
I like to use about 3% silk powder in a mineral make-up application. Why 3%? It's right in the middle of the suggested usage rate, and those little scoops are 0.15 cc (1/32 tsp) (and for some reason that works out to 3% most of the time).
FINISHING POWDER (by volume, not weight)
3 tbsp treated serecite
1 tsp micronospheres
1/5 tsp or 6 scoops calcium carbonate or kaolin clay (for oil control, optional)
1/5 tsp or 6 scoops powdered silk
Put together in a plastic bag and squish and squish and squish until well blended. Please don't put this into a grinder because it will damage the micronospheres. Use this as you would a foundation to brighten up your skin, control oil, and give yourself a nice dewy glow!