Digitise slides and old photos: rescue your family pictures

The Verbraucherzentrale, Germany's consumer advice centre, names water, light and humidity as the main causes of damage to paper and photographs. For photos it sets tighter limits than for paper: temperatures around freezing and relative humidity of no more than 35 per cent (Verbraucherzentrale). It adds that this can hardly be achieved in a normal household and recommends suitable packaging such as archival photo sleeves. According to its advice, lofts are explicitly unsuitable because they get warm in summer, and so are damp cellars. If your slide boxes are kept there, move them out first.

Negatives and slides have a second problem: the film base. A great many films made since the 1920s use cellulose acetate (Image Permanence Institute 1993). This plastic decomposes slowly and releases acetic acid in the process; specialists call it vinegar syndrome. Typical signs are a vinegar smell and buckled, shrunken and brittle film strips. The Image Permanence Institute has calculated when decay becomes measurable in fresh film: at a room temperature of 21 °C and 50 per cent relative humidity, after about 40 years (Image Permanence Institute 1993). Based on the institute's experience, film kept warmer than room temperature degrades in about 30 years, while film stored cooler than room temperature shows no signs of degradation after 50 years (Image Permanence Institute 1993). Once decay has started, the acid released speeds it up further, and in the institute's assessment the remaining useful life at room temperature is short.

Colours do not last either. According to the US FADGI digitisation guidelines, both the orange mask and the dye layers of colour negatives fade over time, influenced among other things by heat and poor processing. Colour negatives made before 1975 do not scan well according to FADGI, whereas films produced after 1995 were already designed to be scanned on digital photographic systems (FADGI). Prints in albums face a danger of their own: the Library of Congress advises against albums with coloured or sticky self-adhesive, so-called magnetic pages (Library of Congress). You can recognise these albums by the clear film stretched over the whole page, holding the pictures on a sticky backing.

There are three routes to digitising: scanning yourself, photographing the originals yourself or commissioning a service. US federal agencies have set out their requirements in the Technical Guidelines for Digitizing Cultural Heritage Materials of the Federal Agencies Digital Guidelines Initiative (FADGI), whose third edition appeared in 2023. For 35 mm slides the guidelines list film scanners, planetary scanners, digital cameras and flatbed scanners as recommended technologies (FADGI). A camera copy is therefore not a makeshift but a recognised route, provided light, focus and alignment are right. The differences lie in the effort, in the control over the result and in whether the originals leave the house.

With a camera copy, the camera replaces the scanner. For slides you need an even light source behind the picture, such as a light panel, and a holder that keeps the slide parallel to the camera. For prints, a table in diffuse daylight or two lamps placed at the sides will do. FADGI names working in a dimly lit room as a way to reduce the effect of ambient light with transparent originals (FADGI). This is how to proceed:

Negatives need an extra step: the image has to be inverted and colour-corrected. FADGI compares digitising negatives to printing them in a darkroom, which depends heavily on the skill and judgement of the person at the controls (FADGI). So save the unedited capture and work on a copy. If you have many negative strips, a scanner that does the inversion itself saves you this step.

Scanning resolution is given in ppi, pixels per inch of the original. FADGI divides quality into four levels from one to four stars. For photographic prints the guidelines set 400 ppi at the third level and 600 ppi at the highest (FADGI). For 35 mm slides and 35 mm negatives the values are far higher because the original is so small: 3,000 ppi at the third and 4,000 ppi at the fourth level (FADGI). These values are written for archives that capture their holdings once and then for decades. For a family collection they are a good yardstick for the pictures that matter to you.

What that means in pixels can be calculated: a 35 mm slide scanned at 3,000 ppi produces a file of around twelve million pixels (own calculation based on FADGI). For individual favourites that will later be printed large or heavily cropped, choose the higher level. For series and snapshots the lower one may be enough, especially as a higher value lengthens every scan and takes up more storage space.

For the file format, the Verbraucherzentrale recommends JPEG or TIFF for image files (Verbraucherzentrale). TIFF saves without loss of quality and suits the archival version but needs considerably more space; JPEG is more compact and opens and shares on any common device. For copies that only serve as a safeguard, the Verbraucherzentrale considers medium quality sufficient. If records are acutely at risk of decay, the quality should be higher, because the copies may become the new originals (Verbraucherzentrale). A slide with vinegar syndrome is exactly that case.

Keeping raw and edited versions apart matters. FADGI requires the master to document the original as it looked at the time of capture and rules out, for example, colourisation, colour restoration and retouching away dust and scratches there; such edits belong in derived versions (FADGI). At home this means keeping one unedited file per picture and storing the colour-corrected, cropped version next to it. There is another reason to rely on widely used formats. The BSI, Germany's Federal Office for Information Security, points out that operating systems and programs are retired at some point, and for home users, in its assessment, after as little as ten years (BSI). The archivists' guide therefore advises avoiding proprietary storage formats and migrating in good time when new common formats emerge (Homa/Schlöder).

Digitising creates a new risk: the pictures now sit on a storage device that can fail. A Bitkom survey shows how common the gap is: 33 per cent of those who use a computer or smartphone privately use no backups at all, and one in five has already lost data because a backup was missing (Bitkom). Only 18 per cent know how to restore the data from a backup (Bitkom). For pictures that have just been digitised with a lot of effort, that is a poor ratio.

The Library of Congress recommends at least two copies of personal photos, stored in locations as physically far apart as practical. You should open the photos at least once a year to check that they can be read, and copy them to new media every five years or when necessary (Library of Congress). The Verbraucherzentrale likewise advises using at least two storage media, ideally in separate places, and warns that CDs, DVDs and Blu-ray discs only remain intact for a few years and that USB sticks are considerably shorter-lived than hard drives (Verbraucherzentrale). If you still have burned photo CDs from the early years of digital photography, move them across at the same time.

How to set up an automatic backup for computer and phone, and which combination of hard drive, NAS and cloud suits you, is explained in the guide to a backup strategy for phone photos. If you use a cloud, encrypt particularly private pictures first; the Verbraucherzentrale explicitly recommends encryption for digital copies of important records (Verbraucherzentrale).

Do not throw the originals away after digitising. They remain the source if a better digitisation is needed later. For storage, the Library of Congress names a relatively dry, cool and stable environment with 30 to 50 per cent relative humidity and no more than 70 °F, around 21 °C (Library of Congress). For colour photographs and film negatives it recommends temperatures of 40 °F or below, around 4 °C (Library of Congress). At home, a cool, dry room away from radiators, lightproof boxes and archival photo sleeves made of tested material are the realistic compromise. According to the Library of Congress, plastic enclosures should not be used for nitrate or acetate-based negatives (Library of Congress).

If you want to give a photo book of old pictures or a digital collection for siblings and grandchildren for Christmas, you need lead time. Sorting, digitising and captioning take longer than the design, so it is worth starting in October. Incidentally, the archivists' guide itself links photo work with the end of the year: if you take fewer than 100 photos a month, you can review your pictures once a year, for example around Christmas (Homa/Schlöder). A timetable for the weeks up to the holidays:

If you give the digital collection together with a new tablet or a digital photo frame for your parents, set the device up before the holidays; how to do that is described in the article Gifting technology: set up devices before Christmas. If grandparents and grandchildren live far apart, the rediscovered pictures can also be looked at together in a video call. The setup is shown in the guide Video calls with the family.