Which comes first?

In the later Middle Ages, when scroll production had become a team work between illuminators and calligraphers, it was the calligrapher who did his work first. He would leave space for initials and other illuminations, and often he would use a diluted ink or a lead point to write instructions for the illuminator. Most calligraphers also do the text before the illuminations. This is because it's so easy to make a mistake when you write. If you just have the text and something goes wrong, you can throw it away and start again. But if you have spent maybe ten, twenty hours or more on the illuminations, it will really hurt to throw it away.

On the other hand, I find that it's more difficult to adapt illuminations to text than the other way around. Text can easily be made bigger or smaller by varying character size, line spacing and wording. Illuminations determine the balance and layout of the scroll and are more difficult to adapt. A diligent artist will of course plan everything ahead and make a dummy scroll where everything fits into place. Not being quite that diligent, I usually begin by doing a detailed pencil version of the illuminations. Then I write the text, and last, I paint the illuminations. This will at least save some work in case a disaster occurs while I'm writing.

In order to be sure that my text fits into the available space, I usually write a not-so-carefully done version of the text on a piece of scrap paper, using the same pen, line spacing etcetera that I intend to use on the real document. This shows me the general size of my text area, so I can know if something needs to be bigger or smaller.