I don't know Zandel, silver equipment are a lot more rare than the bronze counterpart. Also, combining two lvl 1 silver rings brings it to lv 9 instead of lv 10. If you want to use ring on rings, you would need at least over 38 silver rings. (38 silver rings makes 19 lv 9 rings which isn't enough to make lv 40) Also it comes with the added problem of left over bronze equipment if you stick to rings on rings. Personally i have over 32 +10 bracelets compared to 16 +10 rings.
A japanese wiki supposed this to be the rates of mid-level equipment gacha.
We would need to use excess bronze equipment somewhere.
I'm only following this guide which works best for me.
Sourced from :
http://flowerknight.wikia.com/wiki/Equipment