you don't have to...the main difference between junior and primary is that junior can give you max of -8 of the rank of the lowest item you compounded as your result. primary can give you rank 1 (mostly common stone) or any rank in between from the lowest rank item in your compound.

so..this means with junior alchemy you won't get common stone EVER from failing this silvery armor compound. usually, if this fails you will get your lowest rank item back you used in the compound.

also, you should note that junior uses whatever is highest rank item as the base class. so...if you are using primary, make sure you have iron as the first component and fur as the second.

silvery armor = iron net boots + demon gloves + iron net boots

will work for primary alchemy.