BaM, eki, thanks!
For the shield pattern, I looked around for norman and viking shield design on the web, and found these
Skyrim shield mod, used the second one.
First after some edge detect, resize and rotation:
View attachment 77588
Then printing, creating a mask and marking (= stippling with red) some more important area:
View attachment 77589
Then drawing all the lines, first try:
View attachment 77591
This not really good, compared to the original:
View attachment 77590
But not terrible either, finishing the design with VMC Carmine Red and VMC Japanese Uniform:
View attachment 77592
Rim is painted with VMC Red Leather, to connect it to the face, rivets are VMA Steel.
Colors are too saturated and shield is too clean, some weathering and desaturation is still needed.