Greetings cousins from Genevieve,
I had the happy chance to visit with Mistress Caitlin from Harplestane this past weekend. She and her lord Master Otto visited to attend St. Ethelburga's Feast in Thamesreach, and they stayed as our guests.
Some folk don't realize that Caitlin's first area of expertise is not music, but the scribal arts. She's a tremendous resource of knowledge, and I found chatting with her very useful.
Some bits and pieces I learned over the weekend:
Caitlin observed that a weakness of some SCA calligraphy is the lack of distinction between thick and thin lines. Looking at the Luttrell Psalter (which I have on the brain right now), the hairlines and spiral ornaments that come off the thick letters are tiny. She says you can get this fine a line with a quill, but rarely with a nib pen, and so she prefers quills over pens for her own work.
Quills are also better for drawing off a fine line from a corner - again, for the delicate ornaments common in quadrata hands.
Talking about quills - she says that swan quills are better than goose quills, if you have them available. Swans moult (shed their feathers) in the early-mid summer (June/July in UK), and if you're near a river where swans live, you can pick them up after the moult.
Geese, OTOH, have to be plucked, and you don't get as many long primary wing feathers suitable for quills.
She showed Melisende and me a trick for 'seeing' spacing between words in calligraphy: that you turn the scroll upside down, and look along its surface, from the top edge.
When the words are simply blocks of letters (and your brain isn't trying to read them) you can see the spacing between the words better, and can see if it is consistent from line to line. Getting this spacing consistent is an important part of 'getting' the hand.
There may be other clever things I've forgotten - if I think of them I'll add them!