In reply to Type weights theory?:
Thanks for the links guys! Nonetheless I think I wasn't clear enough in explaining what I'm looking for... What I need is the way that bold strokes are extrapolated from, let's say, a light variant. Changing the stroke width in Illustrator is not enough as I've read, it may give equal widths on every stroke but typefaces hardly are so mathematically constructed as I have seen. For example, I took letter p from Myriad Regular, ran the Bold action in FL with a parameter of 40-40, and compared the outline to Myriad Black... needless to say, they are quite different! So, the designer somehow decides how every stroke will relate to the rest, keeping harmony between the shapes and the character of the letterform.
In this same subject, I believe the initial letterforms and interior spaces will dictate how much I can "fatten" a character. Maybe some of you had already seen my font Shket, it has elongated and narrow forms, and some characters like "f" have small curves. Is technically possible to make a bolder version from that letter? If so, How far could I go? Maybe an Extra Black is out of the equation.. but I don't know yet.
Those are the kind of questions I need answers to. I haven't found resources or literature dealing with this technically complex stuff.
Regards!