Short answer: Start with the mount. Labs often printed or pressed the processing month and year on it, which dates the slide to within weeks of the photo. Kodachrome slides exist from 1936, Ektachrome from 1946. Cardboard mounts are typical for older slides, plastic mounts for later ones, and Kodachrome processing ended in December 2010.
Last updated: 2 November 2026. Every year on this page was checked against the museums, archives and photo-history sources listed at the bottom.
A box of slides is often the best-dated part of a family collection, because the date is right there on the mount. Where it is missing, the film name, the mount and the way the colours aged still narrow it down.
Read the mount
- Processing date. Labs often printed information on the mount, such as the frame number and the processing date. Some dates are pressed into the card without ink: hold the mount at an angle under a lamp to read them. The processing date is when the film was developed, usually weeks and sometimes months after the photo.
- Film name. Kodachrome, Ektachrome, Agfachrome or another name on the mount tells you the film, and each film has its own years.
- Material. Processed 35 mm slides were returned in 2 by 2 inch (5 by 5 cm) mounts. Cardboard mounts are typical of the older decades; plastic mounts with printed logos are typical of the 1980s and 1990s.
- Lab or processor. Not every Kodak film was processed by Kodak, so a mount without the Kodak name does not rule out Kodak film.
Know the films
| Film | Years |
|---|---|
| Kodachrome (35 mm slides) | From 1936; Kodachrome II from 1961, Kodachrome-X from 1962; Kodachrome 25 and 64 with process K-14 from 1974; last processing December 2010 |
| Ektachrome | From 1946; 35 mm with process E-2 from 1955 to 1966, E-4 from 1966, E-6 the standard from 1977; discontinued 2012 to 2013, back in 35 mm from 2018 |
Kodak's Carousel projector of 1961 held 80 slides in a round tray. A collection still in Carousel trays is likely from the 1960s or later.
How the colours aged
Kodachrome is known for its stability in the dark: slides made after 1938 often still look much as they did. Ektachrome-type films faded faster, especially the early processes; E-4 slides were expected to last around 30 years. So if two slides from the same box look very different, with one strongly shifted in colour, the faded one is probably an Ektachrome-type film rather than an older Kodachrome. Projection light fades every slide, so the favourite slides are often the most faded.
The picture itself
Inside the range the mount gives, use the clothes, cars and places, just as with prints: see The 1950s (1950 to 1959), The 1960s (1960 to 1969) and The 1970s (1970 to 1979). Scan the slides, or have them scanned, and put the processing date in the file name.
Quick checklist
- A printed or pressed date on the mount? Read it under a lamp at an angle.
- Which film name: Kodachrome, Ektachrome, another brand?
- Cardboard or plastic mount?
- Colours fresh or strongly shifted, compared with others from the same box?
- Still in a Carousel tray (1961 or later)?
Try the free photo date tool
Not sure yet? The free photo date tool asks what you can see (the material, the colour, the edge, the back, a printed year) and turns your answers into a period, with the source behind each year. It needs no account and uploads nothing. For digital photos and scans, read when was this photo taken.
Once you know the year
Write the year in soft pencil on the back, and put it at the start of the file name when you scan it. Then hang it with its date in your palace: in The Memory Palace each photo gets its year, the people in it and the story that goes with it, in a room the family can walk through together. You can start your palace for free.
Date a photo from another decade
Start from the overview: when was this photo taken, or the seven general clues in how to tell when an old photo was taken. All guides on old photos:
- The 1900s (1900 to 1909)
- The 1910s (1910 to 1919)
- The 1920s (1920 to 1929)
- The 1930s (1930 to 1939)
- The 1940s (1940 to 1949)
- The 1950s (1950 to 1959)
- The 1960s (1960 to 1969)
- The 1970s (1970 to 1979)
- The 1980s (1980 to 1989)
- The 1990s (1990 to 1999)
- Cabinet cards and cartes de visite
- Polaroid and instant photos
- Colour prints and negatives
Sources
- Kodak, Photography history (roll film 1889, Brownie 1900, Kodachrome 1935 and for 35 mm slides 1936, Kodacolor 1942, Carousel projector 1961, DC40 digital camera 1995): kodak.com/en/company/page/photography-history
- Wikipedia, Kodachrome (35 mm from 1936, Kodachrome II 1961, K-14 and Kodachrome 25 and 64 in 1974, last processing December 2010): en.wikipedia.org/wiki/Kodachrome
- Wikipedia, Ektachrome (1946; processes E-1 to E-6; discontinued 2012 to 2013, back in 35 mm in 2018): en.wikipedia.org/wiki/Ektachrome
- Virginia Tech University Libraries, Currie Collection, What are slides? (labs often printed the processing date on the mount): curriecollection.blog.lib.vt.edu/what-are-slides