Baader film was invented in 1999 or so. In 1978, mylar was your best bet though for photographic use only, smoked glass could be used (dangerous by eye due to UV). Glass filters came later, then Baader film. Many used welder's glass visually and the dangerous SUN filters sold with cheap telescopes.
Originally Posted by polyglot
You can get photographic Baader film (3) which isn't nearly as many stops so you can use shorter exposures than the visual stuff. You could use multiple layers of Baader film to really bring it down.