Why do old photos turn yellow?

I think one of the greatest inventions in the world is the camera, which can record every bit of our life with our hands and freeze the time at that most meaningful moment. Then we pick up the photo and remember what happened at that time, and the corners of our mouths will smile.

In the last century, our photos were all black and white. In fact, after years of baptism, the previous black-and-white photos will gradually be covered with a faint yellow fog, especially the white border, which will turn yellow after a long time. This is a common phenomenon. In fact, most of the reasons are due to the insufficient washing of the dominant drugs and the residual liquid medicine in the photos. In fact, such yellowed black-and-white photos can better show the historical vicissitudes and sense of time, which is very artistic.

In this era, we are all color photos, and color photos will slowly turn yellow with the passage of time. This is mostly due to the insufficient washing of the dominant drugs in the process of printing, resulting in drug residues in the photos. Color photos will not only turn yellow, but also fade a little, just like colored paper. They will fade after a long time, and of course they may be exposed to strong light for a long time.

In fact, whether it is a black-and-white photo or a color photo, the principle of developing photos is the same, and the principle of photo imaging is the same. There is also a chemical substance in the photo called silver bromide, which is easily oxidized. That is to say, when exposed to oxygen in the air for a long time, a chemical reaction will occur, and another chemical substance will be slowly generated, which will appear yellow in the photo. But often the yellowing of photos is not caused by this factor, but also for a certain photo. However, yellowed photos can show wasted time, which is also a special commemoration.