Is there a rule of thumb to set the space between columns?

Question

I've never heard about a convention to adjust the space between columns in a writing, it seems it depends on aesthetic sense--even in scientific literature---doesn't it?

Answer 1

Quoting Felici, The complete manual of typography, p. 128:

[T]he gutters between columns have to be in tune with both the texture of the type---particularly the leading---and the widths of the margins [...]. The page should appear as a harmonious whole, and the columns should clearly relate to each other to create a sense of their being a unified entity, albeit in several pieces. If the gutters are too wide, the columns look like a series of unrelated text blocks. If the gutters are too narrow, they begin to affect readability, as the eye takes in part of the type from the next column every time it ranges toward the end of the line.

On p. 129, Felici shows an example of justified text columns with too wide gutters and notes "If the text were set ragged right, the effect would be even worse, as ragged margins make gutters seem wider."

In my opinion, the "optimum" column width is about 1.5em to 2em, and the value of \columnsep in the standard classes (10pt) is so small as to affect readability.

Note: The following examples use the default font size of 10pt. As the standard classes don't enlarge the value of \columnsep for the 11pt and 12pt sizes, their readability is affected even worse.

\documentclass[twocolumn]{article}

\usepackage{lipsum}

\usepackage{microtype}

\textheight=180pt

\begin{document}

\lipsum[1-2]

\end{document}

\documentclass[twocolumn]{article}

\usepackage{lipsum}

\usepackage{microtype}

\textheight=180pt

\columnsep=1.6em

\begin{document}

\lipsum[1-2]

\end{document}