HEAVYWEIGHT PAPER: Strong enough to use wet media on both sides of page. Great for artists combining dry media mixed with watercolor. CRAFTED FOR MIXED MEDIA: Double-sized (from non-animal materials) for enhanced wet strength and glowing color. ERASABLE & TOUGH: Withstands multiple erasures and holds up well to layered light washes of wet media. DURABLE: Premium U.S. sewn binding, deluxe covers and heavy-duty art paper equals a sketchbook that is built for serious use. PREMIUM QUALITY: Exceptional features make Stillman & Birn the popular sketchbook choice, cherished by artists of all levels. GAMMA SERIES – SOFTCOVER SKETCHBOOKS Stillman & Birn Gamma Series Softcover Sketchbooks, 150 gsm (Heavyweight), ivory paper, medium grain surface. Suitable for dry media, light wash and ink. Example of recommended usage: working in pencil or ink mixed with watercolor. Softcover bindings are flexible and lightweight and open totally flat. Acid-free, chloride-free, lignin-free.