Hello snagy,
found your message this morning, in Turkey.
Your picture comes from this flag stored at the Bundesbriefmuseum (Le musée des chartes fédérales) at Schwytz in Swtzzerland. You have extracted the picture from a PDF file (
http://www.sz.ch/documents/Fahnen_Fuehrung_6.pdf ) wherein the flag is small on the page, among five flags on the width of 21 cm wide paper.
Unless going and visiting tis museum to concult the flag (assuming it would be available to the public), I see no other way to analyse the content, than using a PC on that image.
Keep in mind that the size of the image in the upper left corner of the flag is very very small, and if scaled down to your 30 mm size flat, would be not marger than 1 square mm , quite uneasy to paint, and even more to see after!!
But I have enlarged the painted section and manipulated a bit the drawing with visibl pixels by adapting the contrast and colours with the following three pics, which could help you to reproduce it.
I cant help more at this point.
Obviousely it represents Jesus on the cross, surrounded by various objects, perhaps representing the statue in a Church or a cathedral with several symblic objects around him.
The red colour of the flag is rather an Alizarin Crimson red, but the background red of the painted small area is rather a bright red, or clear cadmium red tone.
Michel
Pic 1 = rough
Pic 2 = more contrast
pic 3 = further more contrast