The slides Erik used in his lectures are photographs of the original pictures. The film stock used produced positives that were suitable for projection. 35mm glass slide mounts were used to protect the film. The Trust provided me with a CD of scans of the slides which had been done some 10 years previously and regrettably the quality was so poor as to make them un-suitable for use.
I went back to the original slides and by carefully opening one up I discovered that they had been scanned through the slide glass which accounted for some of the indifferent quality, as the film was still stuck down inside the slide holder with the original masking paper. Over the years the glass had developed a semi-opaque film on the inside surface of the glass which was wiped clean.
The slides were then rescanned ans some additional work was carried out in PhotoShop. The results, whilst nor perfect, are better than the originals. Some of the slides have burned-out highlights which are impossible to correct. We are actively searching for the original photographs from which the slides were made. As this was 50 years ago it may take some time to locate them either in RSA or Scotland were most of Erik's papers were stored after his death.