Interesting question, Jasper. It would be useful to have more info about it.

AFAIK, grades are not used just in view of printing quality. Example: text over a yellow background would be clearer if set with a slight darker grade, while over a soft gray background a lighter grade may be the best option. Another possibility is to combine bold from a lighter grade inside texts with a darker bold in titles –to enforce an overall even type colour.

Considering the way many contemporary fonts are built (in order to keep legibility under unfavourable conditions) I thought grades for low quality printing would be subtly changed in two aspects: reduced contrast and weight.

The first change avoids excessive variations that can result from low print quality. In an extreme scenario, thin parts tends to be supressed while the thicker ones tend to be bolder. With less contrast, this effect is reduced –again, due to a more even type colour. The second change ensures thin elements will keep expressiveness. But the thicker change may not be overdone or it will cause the problem you noted.

Althought these two changes are present is some fonts (Mercury, Chronicle), in other the grades are just thicker (Greta, Quiosco, The Serif). So, it seems there is another element to be considered when producing grades.

I think that “low quality printing” in this case means high volume and high speed printing, where ink very briefly touch paper. So, in order to avoid the “vanishing thins” effect Igor mentions, you will use a darker grade (ideally with less stroke contrast too).

Is this 'vanashing thins' effect still an issue today. I know a newspaper printed in Lexicon, which has really thin joins, and it reads great. It might be just me, but I associate this 'vanashing thins' effect with outdated printing technology.

Is this 'vanashing thins' effect still an issue today?

Surely. There are many printed materials still suffering with this. Cheap softcover pocket books and small newspapers are usual examples. And an outdated printing technology is a typical low quality printing situation.

The newspaper you refer seems not to fit the low quality category.

>It might be just me, but I associate this 'van[i]shing thins' effect with outdated printing technology.

>The newspaper you refer seems not to fit the low quality category.

But they move so the paper fast and the ink is so weak, it dries before it goes anywhere. The heart of this question's answer is, how serious you are about designing grades, or at least ones that give a client the right option, or in the case of a more general product, give a range of users the right options.

> The Grade for lo[w] quality printing is usually the thickest (darkest).

I’m not sure where you get this from. Perhaps you are conflating several different concepts in your use of the term “grades.”

The way the term is applied to fonts aimed at newspapers, it usually refers to a range of “weights” (not really weights, per se — hence the specific term “grade”) encompassing both lighter and darker variations. The whole point of a graded series is to be able to select the variation that best suits one’s printing environment.

In some cases, one part of a newspaper might be more heavily inked and benefit from a lighter grade, while another part of the paper might be printed on a higher quality paper (like a photo-heavy insert) and warrant a medium grade. The purpose, in these situations, is to be able to select different grades for different printing conditions so that the overall effect is one of consistency.

Here’s some of the marketing text from Font Bureau’s Readability Series PDF:

“Font Bureau has prepared four closely-spaced grades tuned to the variety of performance to be expected from a range of platemaking technologies and presses. Newspapers using transitional or hybrid output methods should really benefit from use of these fonts. A paper that prints feature or advance pages directly to negatives might do so with one version of the font, while choosing a lighter version for pages that go through paste-up (which typically increases dot gain and weight of the type). Text can be freely moved from section to section without affecting copyfit, since all weights are designed on a single set of character widths. Properly used, these fonts guarantee a consistent quality of text reproduction from front to back. Papers using only one production method still benefit from the grades, as they can choose the weight best matching their inking.”

Hoefler & Frere-Jones speak similarly about their graded series:
http://www.typography.com/fonts/font_overview.php?productLineID=100017
http://www.typography.com/ask/recentTopic.php?rtID=89

Now, if you’re using the term “grade” to refer to different size-specific (so-called “optical”) variants, then the slight weight difference has nothing to do with targeting different printing environments. The fact of the matter is that generally when you have the same typeface reproduced at different sizes, the smaller sizes will tend to appear optically lighter than the larger sizes.

To compensate for this, a size-specific design for smaller sizes will generally have a slightly heavier stem weight compared to a larger variant of the same style.

Of course, stem weight is only one of the adjustments that might be made between size-specific variants. And, as you correctly surmised, if the type is intended for a printing environment with heavy ink gain, then in fact the stem weight on a smaller size might not need to be heavier. With heavy inking, the gain will be proportionally larger for a smaller size type and so, in fact, a lighter stem may be called for under certain circumstances. But these circumstances are fewer and fewer as offset printing quality seems to only get better.

When you’re talking about grades, there are many interrelating factors and it’s difficult to make blanket statements.