diff --git a/zigrtiow/src/main.zig b/zigrtiow/src/main.zig
index 6a294e5..d543205 100644
--- a/zigrtiow/src/main.zig
+++ b/zigrtiow/src/main.zig
@@ -97,6 +97,7 @@ pub fn main() anyerror!void {
     try tmp_world.add(Hittable{ .sphere = Sphere.init(Point3.init(0, -100.5, -1), 100, material_ground) });
     try tmp_world.add(Hittable{ .sphere = Sphere.init(Point3.init(0, 0, -1), 0.5, material_center) });
     try tmp_world.add(Hittable{ .sphere = Sphere.init(Point3.init(-1, 0, -1), 0.5, material_left) });
+    try tmp_world.add(Hittable{ .sphere = Sphere.init(Point3.init(-1, 0, -1), -0.4, material_left) });
     try tmp_world.add(Hittable{ .sphere = Sphere.init(Point3.init(1, 0, -1), 0.5, material_right) });
     const world = Hittable{ .hittable_list = tmp_world };
 
diff --git a/zigrtiow/src/material.zig b/zigrtiow/src/material.zig
index fa2360d..71c42c5 100644
--- a/zigrtiow/src/material.zig
+++ b/zigrtiow/src/material.zig
@@ -1,3 +1,4 @@
+const std = @import("std");
 const vec = @import("./vec.zig");
 const Ray = @import("./ray.zig").Ray;
 const HitRecord = @import("./hittable.zig").HitRecord;
@@ -6,6 +7,7 @@ const Vec3 = vec.Vec3;
 const Color = vec.Color;
 const random_unit_vector = vec.random_unit_vector;
 const random_in_unit_sphere = vec.random_in_unit_sphere;
+const pow = std.math.pow;
 
 pub const Material = union(enum) {
     labertian: Labertian,
@@ -68,6 +70,8 @@ pub const Metal = struct {
     }
 };
 
+var prng = std.rand.DefaultPrng.init(0);
+const rand = prng.random();
 pub const Dielectric = struct {
     ir: f32, // Index of Refraction
 
@@ -80,7 +84,7 @@ pub const Dielectric = struct {
         const sin_theta = @sqrt(1 - cos_theta * cos_theta);
 
         const cannot_refract = refraction_ratio * sin_theta > 1;
-        const direction = if (cannot_refract)
+        const direction = if (cannot_refract or reflectance(cos_theta, refraction_ratio) > rand.float(f32))
             reflect(unit_direction, rec.normal)
         else
             refract(unit_direction, rec.normal, refraction_ratio);
@@ -91,4 +95,10 @@ pub const Dielectric = struct {
             .scattered = scattered,
         };
     }
+    fn reflectance(cosine: f32, ref_idx: f32) f32 {
+        // Use Schlick's approximation for reflectance.
+        var r0 = (1 - ref_idx) / (1 + ref_idx);
+        r0 = r0 * r0;
+        return r0 + (1 - r0) * pow(f32, (1 - cosine), 5);
+    }
 };