From what I gather, sans were originally labeled "Grotesque" and "Gothic" to indicate (what was seen as) their garish, barbaric nature. They were also called "Egyptian" until a confusion in terminology applied the term to slabs.

To illustrate, here is a picture from the European Magazine of 1805, showing their displeasure with these new barbaric types.

Source:
http://typefoundry.blogspot.com/2007/01/nymph-and-grot-update.html

The term Gothic, as used by American typefounders beginning in the nineteenth century, refers to sans-serif type. The term is often misused to classify Blackletter typefaces.

Medieval blackletter being called Gothic was a disparaging term from the Renaissance applied to most, if not all Medieval art and architecture, associating it with the European tribes that had destroyed Rome and the classical civilization the Renaissance was trying to revive. I presume pre-blackletter calligraphy such as uncials was also considered gothic.

19th Century sans-serif type got called Gothic by people who thought it resembled blackletter and Grotesque by people who thought it was ugly. I'm not sure if the term gothic was being used for type and lettering before the Victorian Gothic-revival style of architecture and decorative arts.

Blackletter tends to be called gothic in the context of calligraphy rather than type. Blackletter type being called gothic is often simply due its association with gothic music and fashion, eg. on free font sites.

> I have not been able to find out why san serif fonts such as Franklin Gothic are called Gothic

Linguistic explanation:

In order to describe a new phenomenon, at first, various already existing words denoting something else are used metaphorically to describe the new phenomenon.

Usually, one of these words used metaphorically to describe the new phenomenon becomes the predominant word, and the others words often fall into disuse.

In the case of the new phenomenon of the sans serif typefaces at the beginning of the 19th century, three metaphorical words describing something else were used to describe the new phenomenon of sans serif typefaces:

- "doric"
- "grotesque"
- "gothic"

The metaphorical word "doric" fell into disuse both in America and in Europe and is no longer used for sans serif typefaces at all, but it is still mentioned in Webster's Third New International Dictionary of 1961.

The metaphorical word "grotesque" became the predominant word in Europe, especially in Britain and Germany, for describing sans serif typefaces metaphorically.

The metaphorical word "gothic" became the predominant word in America for describing sans serif typefaces metaphorically.

If you look into the British encyclopedia "Glaister's Glossary of the Book", second edition 1979, sub voce "gothic", "grotesque", "doric", you will discover

- that the word "gothic" is not used metaphorically for sans serif fonts,
- that the word "grotesque" is used metaphorically for sans serif fonts,
- that the word "doric" is no longer mentioned at all.

For those who are not familiar with French, it should be mentioned that e.g. the "Dictionnaire de l'édition. Français-Anglais. Anglais-Français" by Philippe Schuwer, published in 1977, did not yet contain the word "sans serif" as a French word.

The expressions "Sans", "Serif", "Sanserif", "Sans serif", "Sans-serif" etc. were not listed at all in the French section of this bilingual dictionary of 1977.

The expressions "Sans serif", "Serif" and "Sanserif" were only found in the English section of this bilingual dictionary, with translations into French words.

This means that before the computer and internet age, the French did not use the so-called "French" expression "sans serif".

To increase the complexity of the problem and partially explain what Justin_Ch wrote above: “Gothic” as a denomination for blackletter (handwritten or printed) only refers to a certain form of blackletter, which is also termed Textura or Textualis (see http://en.wikipedia.org/wiki/Blackletter#Textualis). Fraktur is another branch of broken letterform.
For a start in books on the topic I'd recommend “Blackletter: Type and National Identity”, ed. by Peter Bain/Paul Shaw, or if you read German, Albert Kapr’s “Fraktur. Form und Geschichte der gebrochenen Schriften”. For the sanserif Gothic, James Mosley’s “The Nymph and the Grot. The revival of the sanserif letter” was already mentioned.

@Ivan: …these new barbaric types…

They weren't types then (1805), only lettering.
The sample you show is a block cut inserted into type matter, and the artist responsible has created a deliberately crude parody.
Such was the opprobrium attached to this putatively primitive style that type founders were slow to render it in print, long after its use had become widespread in other media.

Is there a term for the phenomenon whereby somebody or something acquires the term by which it is derided, as a badge of honor? It's an ancient practice; the Cynics of Ancient Greece were quite literally dogs.

I suspect there was an element of irony at play, as type founders proudly adopted the name Gothic, by which their clients half-mockingly referred to the new style.

I'm pretty sure "Gothic" referring to blackletter comes of a persistent modern association with Gothic Horror by the layman.

The use of "Gothic" to refer to blackletter is attributed to Lorenzo Valla (in his De elegantiis latinae linguae) by Elizabeth Eisenstein (in The Printing Press As an Agent of Change, 1979, citing earlier authors such as Paul Frankl).

For reference, "gotico" is still the proper way to refer to blackletter in Italian.

In Latvia blackletter started to fade out around 1930. So the books and newspapers printed before were and still are referred to as printed with "Gothic letters" - Gotu burti. And if you mention to anybody "gothic" the first association is "Blackletter". Sans Serif were usually referred as Block letters - Bloka burti.

The Russian for blackletter is готический шрифт [goticheskii shrift]. Predictably, the names of American sans-serifs are transliterated:

Авангард Готик

Белл Готик

Леттер Готик

Ньюс Готик

Франклин Готик, etc.

Sans-serifs are commonly known as рубленые [rublenye, ‘hewn’] or гротески [groteski]. One sans-serif variety used to be called древний [drevnii, ‘antique’].

Thank you all for your erudition and references. Very helpful!