I am not an expert at all in that type of job, but if it's such a big jproject, my instinct tells me you could ask for a portion to start (which can cover a lot of material cost) and the remaining when completed. Again, I don't deal with these type of jobs, so let's see what others might suggest...
All the best!
Aurore Simonnet - Scientific Illustrator
NASA EPO - Sonoma State University [log in to unmask]http://epo.sonoma.edu
I usually do smallish jobs and just ask for payment upon delivery. However, I've been commissioned to make a large painting commemorating a capital campaign
and it will take me quite some time and involve a good chunk of money. Stages in the project are to finalize the list of species that will be painted, complete a detailed rendering of the composition that they can make a banner with, and then the final piece. Should I ask for a portion of the payment at each of those stages? Just the banner and final piece stages? What do others do?