Black ink fading

[nablator]

I'm no expert, but the tracing of the nymph's heads looks to be done with a finer nib than the writing of the month names.

I often wondered how they did those incredibly sharp lines with a quill: same width at all angles. The writing is sometimes incredibly thin too. For example You are not allowed to view links. Register or Login to view. starting line 15, with dark ink, at 3rd word qokeochy. Is there any example of such thin drawing and writing in any other medieval ms.?