I don't know anything about knapsacks, but I recently took pictures of some National Archives documents that show shipments of "painted knapsacks" to many different units in 1811/12. What interested me was the fact that often the unit commander at that particular time was named. Even though there are probably many other sources of that information, it is all new to me.
I'm posting links to the images here so perhaps when someone answers your question, they'll explain painted vs. unpainted knapsacks for my benefit.
I'm sorry the images are hard to read, a good magnifier usually works, or you can zoom in with controls on your browser. If you really want to see the detail, you can save the picture to your computer and use Microsoft Photo Editor or similar program to blow up the image without much loss of clarity.
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