Research of designs and inspiration:

The styles of rings I would focus on: antique and simple accurate.

1) Brilliant Earth

http://www.brilliantearth.com/antique-engagement-rings/

2) Verragio Collection

http://www.youtube.com/watch?v=H3kGr-SGiXM

http://www.youtube.com/watch?v=39pxAdaqeFI

3) Rings San Diego California – Vanessa Nicole Jewels Wedding Rings

http://www.youtube.com/watch?v=A1O_pnxYySg

4) The knot

http://www.theknot.com/gallery/wedding-rings/results/?Engagement%20Ring%20Styles=Vintage+Styles

Research on materials:

Gold and platinum are preferred for engagement rings, but common metal types such as titanium, silver, and stainless steel are also used for engagement rings.

Most popular colors of stones –

http://www.youtube.com/watch?v=YizGfSIisJE