I remember spending a day (or possibly longer) sitting at a table putting caps with brushes fixed in them into the filled mascara tubes. We had a pile of grey, cardboard boxes which were just big enough for a single mascara. These were flat when they arrived and it was quite a fiddly job to manipulate them into box/tube shapes and then fold the little end flaps in without mangling them up or tearing them.
I’ve found a great photo of ladies filling mascara tubes here: http://www.flickr.com/photos/36618304@N05/7698859690/
“Holloways of Lavenham Cosmetic Manufacture no high tech machinery here Eileen Pryke filling tubes of Evette Mascara destination Woolworth while her friend screws on the tops probably mid to late 80s copyright E Pryke”