Alternate "r" in 16th century Spanish

[websentia]

I find in a mid-16th century Spanish printed publication the use of two lower case r's.  See attached PNG. "El tercero libro" demonstrates this where a fairly standard lower case "r" is used int "tercero" whereas in a different character is used in "libro".

Does anyone know the context in which one is chosen instead of the other?

Does anyone know if this is a common or historic convention and if a particular Unicode character would be used for this today?

I find consistant usage of each character in words that are repeated but cannot decipher a rule regarding usage either by proximity to consonants or vowels, beginning or ending of words or syllables, use in nouns or verbs, etc, etc.  Perhaps it is related to pronunciation but I can't establish that since I don't speak Renaissance Spanish.

[Ramón_G_Castañeda]

Because you sent your picture as an attachment, it's in the virus scanning cue, where it will languish for hours, days, weeks or months in these miserable new forums.

If you embed your images in your post through the camera icon in the formatting bar of the reply editor, they will be viewable instantly.

then:

[Ramón_G_Castañeda]

There is no difference in pronunciation or orthography between those two instances of "r" in Spanish, not now and not four centuries ago.

You must be looking at alternative characters of a typeface or calligraphy script, such as exist for many modern typefaces, and their use is entirely up to the typesetter or writer.  I would definitely not use any such alternative r.

[websentia]

Thanks for your replies and I'm glad the image made it throught finally.

This is a historic anthology of music for vihuela. I am creating fonts to replicate this style in modern software. For those who feel strongly about correctness, I would like to have their options in good order. It is very odd to me because every instance of the word "libros" uses the same style "r".  It seems that when the "r" follows  b, p, or o, it uses the alternate version as in "libro". Perhaps the reason is for visual clarity wheh following a rounded glyph.  Whatever the reason, it seems consistant.

[John_Nolan-ylAnVM · Accepted solution]

See mention of the "ragged r" here:

http://ilovetypography.com/2009/06/03/genuine-revivals-matthew-carter-on-typeface-revivals/#more-5475

[websentia]

Ah!  The light shines!  Thank you for this information. I suppose I was close to seeing this but not knowing if this my imagination or the truth.  Thank you so much.

[Ramón_G_Castañeda]

More here:

http://typophile.com/node/37002

[websentia]

Very nice. This is fascinating. I wish I had all this when I was a lad.