Grain Stain Exterior Semi-Transparent Oil Stain. Allows the natural wood texture to show through. Grain Stain Semi-Transparent Oil Stain is a high quality deep penetrating exterior oil stain designed to protect and enrich the natural beauty of wood, allowing the natural wood texture to show through. Grain Stain protects wood with its water-repellent properties, causing water to bead up instead of penetrating the surface.