Thank you Uwe, after reading your reply I consider that I don't know enough about ink to risk it, and as you say, they are readily available and cheap enough.

An update on the re-inking of ribbons for an Empire 1 (aka Wellington or Klein Adler): I agree that trying to re-ink a standard ribbon is never justified when new ribbons are available at low prices but started down the re-inking route for the non-standard width Empire ribbon (about 20mm wide) as I was struggling to obtain a new ribbon.
A mix of metal stamp ink and glycerine had been suggested but even at around a 50/50 mix the ink was still very gloopy and difficult to apply. The result was inconsistent and the print quality very heavy.
I also had a dry, old stock time clock recorder ribbon of the correct width and had read about breathing new life into dry ribbons using WD40. This was easier to do and after leaving it to soak in for a couple of days, gave a reasonable print quality, although more faint than a standard ribbon. Still not fully satisfied, I purchased a new ribbon from the only known supplier of 20mm ribbons (in the Netherlands). The print quality with this ribbon was also faint, suggesting that this might be an issue with time clock recorder ribbons? 
I fitted a standard width ribbon to test out the print quality, accepting that this would only print upper case letters and numerals - the print quality was darker but confirmed that some of the fading on some letters was more to do with the typewriter itself! According to the database, the typewriter is 100 years old, so it’s not doing too badly...!