Science of pH

pH seems like a simple concept but it’s actually relatively complicated. Let’s correct some misunderstandings that I have seen recently.

1. There is nothing magical about a pH of 7. pH 7.0 is generally defined as neutral; however that doesn’t mean there is something drastically wrong at a pH of 6.9 or 7.1. All pH measurements have some error in them – typically 0.1 to 0.2 pH units. Because of buffering, many relatively safe materials have a pH somewhat above 7, with a pH range of 7.0 to 9.5 generally recognized as safe.
2. pH is not limited to values between 0 and 14. I had a discussion with my son’s science teacher about this misconception. pH is a logarithmic scale and as such is not inherently limited to a specific value range. pH can extend below zero and above 14, although the majority of common materials do fall within this range. Highly acidic hot springs near Ebeko volcano have an estimated pH of -1.7 and at the other end of the scale, a saturated base solution has a pH of about 15. (See Negative pH Does Exist.)
3. Buffered paper is fine for color photographs. The recommendation to avoid buffered paper with color photographs crept into some early photographic standards for no clear reason, and well meaning writers have continue to repeat it. In fact buffered paper is safer than non-buffered for all materials since it protects against acids that may be present in the air.

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