These days we have a wide choice of marking pens and pencils, including the wash out ones, but it hasn't always been so easy. I came across this information the other day on a little newspaper clipping my mother cut out, presumably from the "Advertiser", though not sure when. It was one of a number tucked into one of her travel diaries from the 1970s.
"Making transfer ink for embroidery designs - Mix equal quantities of castor sugar and laundry blue which has been ground finely. Store in a screw-top jar and when required for use mix a little with cold water to the consistency of writing ink. Trace over the outline of the design, using an ordinary clean nib".
So, if you worry about what is actually in the commercial ones you could try this. It just might be difficult getting hold of the laundry blue and an 'ordinary' nib now!
Some of the other clippings were interesting too - cleaning silver, preserving autumn leaves, waterproof shoe polish and the 7 Wonders of the World.
This picture is unrelated - just thought it was worth sharing. What is it? A floret of a bromeliad flower.