How to draw a 3D helm

How to draw realistically steel, iron, chrome objects. How to draw a 3D helmet with mixed media on gray paper. 3D drawing by Marcello Barenghi http://www.marcellobarenghi.com

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Music: "pink-garbage" royalty-free music from https://www.audioblocks.com/
Final picture: http://www.marcellobarenghi.com/2013/06/spanish-helmet.html
Used materials:
pasteboard (vegetal paper - light gray) 35x25 cm 1,5 mm, typically used for frames, cartonnage and binding),
9B, 7B and B pencils (Caran d'Ache grafwood),
paper stomp,
Ecoline,
colored pencils (Caran d'Ache Supracolor Soft Artis),
fibre tip pens (Staedtler Noris Club 320 Double Ended Fibre Tip Pens),
markers (Tria Letraset),
pens (Pitt artist pen Faber-Castell and Stabilo Felt Tip),
black and white acrylic (Decoart and Pebeo),
white gel pen (Pentel Hybrid Gel Grip k118-LW),
brush Lefranc & Bourgeois 2 INT 1 polyamide effilé-tapered polyamid
Time taken: 3 hours and 25 minutes