Carlsson's is a dark brown hard rosin used by orchestra pros. Made in Sweden by the Hart Family for many generations. Season for use is All Weather in most climates. Because Carlsson's bass rosin is another of the Hard Rosin Formulas, we sometimes rosin our new bass bows with Carlsson's first, then layer over the top with softer rosin like Pop's. This hard bass rosin under softer rosin combo gives brand new bow hair noticeably better grip much more quickly. Later, The Carlsson's will absorb much of the extra moisture in the Pop's so the remaining rosin in the bow dries more quickly, a real plus in our Bow Trial Room, where quick refurbishing of bows is crucial to accurate, effective testing.