diff --git a/src/material.h b/src/material.h
index cae78f3..82cd311 100644
--- a/src/material.h
+++ b/src/material.h
@@ -29,14 +29,55 @@ class lambertian : public material{
 
 class metal : public material{
     public:
-        metal(const color& a) : albedo(a){}
+        metal(const color& a, double f) : albedo(a), fuzz(f < 1 ? f : 1){}
 
         virtual bool scatter(const ray& r_in, const hit_record& rec, color& attenuation, ray& scattered)const override {
             vec3 reflected = reflect(unit_vector(r_in.direction()), rec.normal);
-            scattered = ray(rec.p, reflected);
+            scattered = ray(rec.p, reflected + fuzz * random_in_unit_sphere());
             attenuation =albedo;
             return (dot(scattered.direction(), rec.normal) > 0);
         }
     public:
         color albedo;
+        double fuzz;
+};
+
+class dielectric : public material{
+    public:
+        dielectric(double index_of_refraction) : ir(index_of_refraction){}
+
+        virtual bool scatter (const ray& r_in, const hit_record& rec, color& attenuation, ray& scattered) const override{
+            attenuation = color(1.0,1.0,1.0);
+            double refraction_ratio = rec.front_face ? (1.0/ir) : ir;
+
+            vec3 unit_direction = unit_vector(r_in.direction());
+
+            double cos_theta = fmin(dot(-unit_direction, rec.normal), 1.0);
+            double sin_theta = sqrt(1.0 - cos_theta * cos_theta);
+            bool cannot_refract = refraction_ratio * sin_theta > 1.0;
+            vec3 direction;
+
+            if(cannot_refract || reflectance(cos_theta, refraction_ratio) > random_double()){
+                // Must reflect
+                direction = reflect(unit_direction, rec.normal);
+            } else {
+                // can refract 
+                direction = refract(unit_direction, rec.normal, refraction_ratio);
+            }
+
+            scattered = ray(rec.p, direction);
+
+            return true;
+        }
+
+    public:
+        double ir;
+
+    private:
+        static double reflectance(double cosine, double ref_idx){
+            // use Schlik's approximation
+            auto r0 = (1-ref_idx) / (1+ref_idx);
+            r0 = r0*r0;
+            return r0 + (1-r0)*pow((1-cosine), 5);   
+        }
 };
\ No newline at end of file
diff --git a/src/program.cpp b/src/program.cpp
index b705823..ce04180 100644
--- a/src/program.cpp
+++ b/src/program.cpp
@@ -41,14 +41,15 @@ int main ()
     hittable_list world;
 
     auto material_ground = make_shared<lambertian>(color(0.8,0.8, 0.0));
-    auto material_center = make_shared<lambertian>(color(0.7,0.3,0.3));
-    auto material_left = make_shared<metal> (color(0.8,0.8,0.8));
-    auto material_right = make_shared<metal>(color(0.8,0.6,0.2));
+    auto material_center = make_shared<lambertian>(color(0.1, 0.2, 0.5));
+    auto material_left = make_shared<dielectric> (1.5);
+    auto material_right = make_shared<metal>(color(0.8,0.6,0.2), 0.0);
     
 
     world.add(make_shared<sphere>(point3(0,-100.5,-1), 100.0, material_ground));
     world.add(make_shared<sphere>(point3(0,0,-1), 0.5,  material_center));
     world.add(make_shared<sphere>(point3(-1.0, 0.0, -1), 0.5, material_left));
+    world.add(make_shared<sphere>(point3(-1.0, 0.0, -1), -0.4, material_left));
     world.add(make_shared<sphere>(point3(1.0, 0.0, -1), 0.5, material_right));
 
 
diff --git a/src/vector3.h b/src/vector3.h
index 42d9038..1850bec 100644
--- a/src/vector3.h
+++ b/src/vector3.h
@@ -130,4 +130,11 @@ vec3 random_in_hemisphere (const vec3& normal){
 
 vec3 reflect (const vec3& v, const vec3& n){
     return v -2 *dot(v,n) *n;
+}
+
+vec3 refract(const vec3& uv, const vec3& n, double etai_over_etat){
+    auto cos_theta = fmin(dot(-uv,n), 1.0);
+    vec3 r_out_perp = etai_over_etat * (uv + cos_theta*n);
+    vec3 r_out_parallel = -sqrt(fabs(1.0 - r_out_perp.length_squared())) * n;
+    return r_out_perp + r_out_parallel; 
 }
\ No newline at end of file