diff --git a/examples/colorful.yaml b/examples/colorful.yaml
index 7dcca98..6ed76fa 100644
--- a/examples/colorful.yaml
+++ b/examples/colorful.yaml
@@ -47,6 +47,9 @@ objects:
         r: 1.0
         g: 1.0
         b: 1.0
+      # Optional fields (go together)
+      #transparency: 0.5
+      #index: 1.5
     texture:
       type: uniform
       color:
@@ -71,7 +74,7 @@ objects:
         g: 1.0
         b: 1.0
       # Optional field
-      # reflectivity: 0.0
+      #reflectivity: 0.0
     texture:
       type: uniform
       color:
diff --git a/examples/scene.yaml b/examples/scene.yaml
index a6b4ab5..d65f02b 100644
--- a/examples/scene.yaml
+++ b/examples/scene.yaml
@@ -35,7 +35,6 @@ objects:
       type: uniform
       diffuse: {r: 0.5, g: 0.5, b: 0.5}
       specular: {r: 1., g: 1., b: 1.}
-      reflectivity: 0.5
     texture:
       type: uniform
       color: {r: 0.25, g: 0.5, b: 1.}
diff --git a/src/core/light_properties.rs b/src/core/light_properties.rs
new file mode 100644
index 0000000..c76cab9
--- /dev/null
+++ b/src/core/light_properties.rs
@@ -0,0 +1,124 @@
+use super::color::LinearColor;
+use serde::Deserialize;
+
+#[derive(Debug, PartialEq, Clone, Deserialize)]
+#[serde(untagged)]
+pub enum ReflTransEnum {
+    Transparency {
+        /// The transparency coefficient.
+        #[serde(rename = "transparency")]
+        coef: f32,
+        /// The diffraction index.
+        index: f32,
+    },
+    Reflectivity {
+        /// The reflectivity coefficient.
+        #[serde(rename = "reflectivity")]
+        coef: f32,
+    },
+}
+
+/// A structure holding all the physical proprerties relating to light at a point.
+#[derive(Debug, PartialEq, Clone, Deserialize)]
+pub struct LightProperties {
+    /// The diffuse component.
+    pub diffuse: LinearColor,
+    /// The specular component.
+    pub specular: LinearColor,
+    /// The transparency or reflectivity properties.
+    #[serde(flatten)]
+    pub refl_trans: Option<ReflTransEnum>,
+}
+
+impl LightProperties {
+    pub fn new(
+        diffuse: LinearColor,
+        specular: LinearColor,
+        refl_trans: Option<ReflTransEnum>,
+    ) -> Self {
+        LightProperties {
+            diffuse,
+            specular,
+            refl_trans,
+        }
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn new_works() {
+        let diffuse = LinearColor::new(0.25, 0.5, 1.);
+        let specular = LinearColor::new(0.75, 0.375, 0.125);
+        let refl_trans = Some(ReflTransEnum::Reflectivity { coef: 0.5 });
+        let properties =
+            LightProperties::new(diffuse.clone(), specular.clone(), refl_trans.clone());
+        assert_eq!(
+            properties,
+            LightProperties {
+                diffuse,
+                specular,
+                refl_trans,
+            }
+        )
+    }
+
+    #[test]
+    fn deserialization_without_refl_trans_works() {
+        let yaml = r#"
+            diffuse: {r: 1.0, g: 0.5, b: 0.25}
+            specular: {r: 0.25, g: 0.125, b: 0.75}
+        "#;
+        let properties: LightProperties = serde_yaml::from_str(yaml).unwrap();
+        assert_eq!(
+            properties,
+            LightProperties::new(
+                LinearColor::new(1., 0.5, 0.25),
+                LinearColor::new(0.25, 0.125, 0.75),
+                None
+            )
+        )
+    }
+
+    #[test]
+    fn deserialization_with_reflection_works() {
+        let yaml = r#"
+            diffuse: {r: 1.0, g: 0.5, b: 0.25}
+            specular: {r: 0.25, g: 0.125, b: 0.75}
+            transparency: 0.5
+            index: 1.5
+        "#;
+        let properties: LightProperties = serde_yaml::from_str(yaml).unwrap();
+        assert_eq!(
+            properties,
+            LightProperties::new(
+                LinearColor::new(1., 0.5, 0.25),
+                LinearColor::new(0.25, 0.125, 0.75),
+                Some(ReflTransEnum::Transparency {
+                    coef: 0.5,
+                    index: 1.5
+                })
+            )
+        )
+    }
+
+    #[test]
+    fn deserialization_with_transparency_works() {
+        let yaml = r#"
+            diffuse: {r: 1.0, g: 0.5, b: 0.25}
+            specular: {r: 0.25, g: 0.125, b: 0.75}
+            reflectivity: 0.25
+        "#;
+        let properties: LightProperties = serde_yaml::from_str(yaml).unwrap();
+        assert_eq!(
+            properties,
+            LightProperties::new(
+                LinearColor::new(1., 0.5, 0.25),
+                LinearColor::new(0.25, 0.125, 0.75),
+                Some(ReflTransEnum::Reflectivity { coef: 0.25 })
+            )
+        )
+    }
+}
diff --git a/src/core/mod.rs b/src/core/mod.rs
index 849639a..e516fb5 100644
--- a/src/core/mod.rs
+++ b/src/core/mod.rs
@@ -6,3 +6,6 @@ pub use color::*;
 
 pub mod film;
 pub use film::*;
+
+pub mod light_properties;
+pub use light_properties::*;
diff --git a/src/material/mod.rs b/src/material/mod.rs
index f946891..8be6f84 100644
--- a/src/material/mod.rs
+++ b/src/material/mod.rs
@@ -1,18 +1,7 @@
-use super::core::color::LinearColor;
+use super::core::LightProperties;
 use super::Point2D;
 use serde::Deserialize;
 
-/// A structure holding all the physical proprerties relating to light at a point.
-#[derive(Debug, PartialEq, Clone)]
-pub struct LightProperties {
-    /// The diffuse component.
-    pub diffuse: LinearColor,
-    /// The specular component,
-    pub specular: LinearColor,
-    /// The reflectivity coefficient,
-    pub reflectivity: f32,
-}
-
 /// All the existing `Material` implementation.
 #[serde(tag = "type")]
 #[serde(rename_all = "lowercase")]
diff --git a/src/material/uniform.rs b/src/material/uniform.rs
index de999b9..73060b7 100644
--- a/src/material/uniform.rs
+++ b/src/material/uniform.rs
@@ -1,88 +1,53 @@
-use super::LightProperties;
 use super::Material;
-use crate::core::color::LinearColor;
+use crate::core::LightProperties;
 use crate::Point2D;
 use serde::Deserialize;
 
 /// A material with the same characteristics on all points.
 #[derive(Clone, Debug, PartialEq, Deserialize)]
 pub struct UniformMaterial {
-    diffuse: LinearColor,
-    specular: LinearColor,
-    #[serde(default)]
-    reflectivity: f32,
+    #[serde(flatten)]
+    properties: LightProperties,
 }
 
 impl UniformMaterial {
-    pub fn new(diffuse: LinearColor, specular: LinearColor, reflectivity: f32) -> Self {
-        UniformMaterial {
-            diffuse,
-            specular,
-            reflectivity,
-        }
+    pub fn new(properties: LightProperties) -> Self {
+        UniformMaterial { properties }
     }
 }
 
 impl Material for UniformMaterial {
     fn properties(&self, _: Point2D) -> LightProperties {
-        LightProperties {
-            diffuse: self.diffuse.clone(),
-            specular: self.specular.clone(),
-            reflectivity: self.reflectivity,
-        }
+        self.properties.clone()
     }
 }
 
 #[cfg(test)]
 mod test {
     use super::*;
+    use crate::core::color::LinearColor;
+    use crate::core::ReflTransEnum;
 
     #[test]
     fn new_works() {
-        let diffuse = LinearColor::new(0., 0.5, 0.);
-        let specular = LinearColor::new(1., 1., 1.);
-        let reflectivity = 0.5;
-        let mat = UniformMaterial::new(diffuse.clone(), specular.clone(), reflectivity);
-        assert_eq!(
-            mat,
-            UniformMaterial {
-                diffuse,
-                specular,
-                reflectivity
-            }
-        )
+        let properties = LightProperties {
+            diffuse: LinearColor::new(0., 0.5, 0.),
+            specular: LinearColor::new(1., 1., 1.),
+            refl_trans: None,
+        };
+        let mat = UniformMaterial::new(properties.clone());
+        assert_eq!(mat, UniformMaterial { properties })
     }
 
-    fn simple_material() -> impl Material {
-        UniformMaterial::new(
-            LinearColor::new(0.5, 0.5, 0.5),
+    #[test]
+    fn properties_works() {
+        let properties = LightProperties::new(
+            LinearColor::new(0., 0.5, 0.),
             LinearColor::new(1., 1., 1.),
-            0.5,
-        )
-    }
-
-    #[test]
-    fn diffuse_works() {
-        let mat = simple_material();
-        assert_eq!(
-            mat.properties(Point2D::origin()).diffuse,
-            LinearColor::new(0.5, 0.5, 0.5)
-        )
-    }
-
-    #[test]
-    fn specular_works() {
-        let mat = simple_material();
-        assert_eq!(
-            mat.properties(Point2D::origin()).specular,
-            LinearColor::new(1., 1., 1.)
-        )
-    }
-
-    #[test]
-    fn reflectivity_works() {
-        let mat = simple_material();
-        assert!(mat.properties(Point2D::origin()).reflectivity - 0.5 < std::f32::EPSILON)
+            None,
+        );
+        let mat = UniformMaterial::new(properties.clone());
+        assert_eq!(mat.properties(Point2D::origin()), properties)
     }
 
     #[test]
@@ -95,11 +60,11 @@ mod test {
         let material: UniformMaterial = serde_yaml::from_str(yaml).unwrap();
         assert_eq!(
             material,
-            UniformMaterial::new(
+            UniformMaterial::new(LightProperties::new(
                 LinearColor::new(1., 0.5, 0.25),
                 LinearColor::new(0.25, 0.125, 0.75),
-                0.25
-            )
+                Some(ReflTransEnum::Reflectivity { coef: 0.25 })
+            ))
         )
     }
 }
diff --git a/src/render/object.rs b/src/render/object.rs
index 61c9af5..c208c0e 100644
--- a/src/render/object.rs
+++ b/src/render/object.rs
@@ -45,6 +45,7 @@ impl BHShape for Object {
 mod test {
     use super::*;
     use crate::core::color::LinearColor;
+    use crate::core::LightProperties;
     use crate::material::UniformMaterial;
     use crate::shape::Sphere;
     use crate::texture::UniformTexture;
@@ -52,11 +53,11 @@ mod test {
 
     fn simple_object() -> Object {
         let shape = Sphere::new(Point::new(5., 0., 0.), 1.);
-        let material = UniformMaterial::new(
+        let material = UniformMaterial::new(LightProperties::new(
             LinearColor::new(0.5, 0.5, 0.5),
             LinearColor::new(1., 1., 1.),
-            0.5,
-        );
+            None,
+        ));
         let texture = UniformTexture::new(LinearColor::new(0.25, 0.5, 1.));
         Object::new(shape.into(), material.into(), texture.into())
     }
@@ -64,11 +65,11 @@ mod test {
     #[test]
     fn new_works() {
         let shape = Sphere::new(Point::new(5., 0., 0.), 1.);
-        let material = UniformMaterial::new(
+        let material = UniformMaterial::new(LightProperties::new(
             LinearColor::new(0.5, 0.5, 0.5),
             LinearColor::new(1., 1., 1.),
-            0.5,
-        );
+            None,
+        ));
         let texture = UniformTexture::new(LinearColor::new(0.25, 0.5, 1.));
         assert_eq!(
             simple_object(),
@@ -93,7 +94,6 @@ mod test {
               type: uniform
               diffuse: {r: 0.5, g: 0.5, b: 0.5}
               specular: {r: 1., g: 1., b: 1.}
-              reflectivity: 0.5
             texture:
               type: uniform
               color: {r: 0.25, g: 0.5, b: 1.}
diff --git a/src/render/scene.rs b/src/render/scene.rs
index 9d113a3..b8322d5 100644
--- a/src/render/scene.rs
+++ b/src/render/scene.rs
@@ -1,7 +1,7 @@
 use super::{light_aggregate::LightAggregate, object::Object};
 use crate::{
-    core::{Camera, LinearColor},
-    material::{LightProperties, Material},
+    core::{Camera, LightProperties, LinearColor, ReflTransEnum},
+    material::Material,
     shape::Shape,
     texture::Texture,
     {Point, Vector},
@@ -20,6 +20,7 @@ pub struct Scene {
     bvh: BVH,
     aliasing_limit: u32,
     reflection_limit: u32,
+    diffraction_index: f32,
 }
 
 impl Scene {
@@ -29,6 +30,7 @@ impl Scene {
         mut objects: Vec<Object>,
         aliasing_limit: u32,
         reflection_limit: u32,
+        diffraction_index: f32,
     ) -> Self {
         let bvh = BVH::build(&mut objects);
         Scene {
@@ -38,6 +40,7 @@ impl Scene {
             bvh,
             aliasing_limit,
             reflection_limit,
+            diffraction_index,
         }
     }
 
@@ -82,7 +85,13 @@ impl Scene {
         let direction = (pixel - self.camera.origin()).normalize();
         self.cast_ray(Ray::new(pixel, direction))
             .map_or_else(LinearColor::black, |(t, obj)| {
-                self.color_at(pixel + direction * t, obj, direction, self.reflection_limit)
+                self.color_at(
+                    pixel + direction * t,
+                    obj,
+                    direction,
+                    self.reflection_limit,
+                    self.diffraction_index,
+                )
             })
     }
 
@@ -105,6 +114,7 @@ impl Scene {
         // NOTE(Bruno): should be written using iterators
         let mut shot_obj: Option<&Object> = None;
         let mut t = std::f32::INFINITY;
+        // NOTE: we don't care about all objects... Only the closest one
         for object in self.bvh.traverse(&ray, &self.objects).iter() {
             match object.shape.intersect(&ray) {
                 Some(dist) if dist < t => {
@@ -123,31 +133,82 @@ impl Scene {
         object: &Object,
         incident_ray: Vector,
         reflection_limit: u32,
+        diffraction_index: f32,
     ) -> LinearColor {
-        let normal = object.shape.normal(&point);
-        let reflected = reflected(incident_ray, normal);
         let texel = object.shape.project_texel(&point);
-
         let properties = object.material.properties(texel);
         let object_color = object.texture.texel_color(texel);
 
-        self.illuminate(point, object_color, &properties, normal, reflected)
-            + self.reflection(point, &properties, reflected, reflection_limit)
+        let normal = object.shape.normal(&point);
+        let reflected = reflected(incident_ray, normal);
+
+        let lighting = self.illuminate(point, object_color, &properties, normal, reflected);
+        match properties.refl_trans {
+            None => lighting,
+            Some(ReflTransEnum::Transparency { coef, index }) => {
+                // Calculate the refracted ray, if it was refracted
+                refracted(incident_ray, normal, diffraction_index, index).map_or_else(
+                    // Total reflection
+                    || self.reflection(point, 1., reflected, reflection_limit, diffraction_index),
+                    // Refraction
+                    |r| {
+                        self.refraction(point, coef, r, reflection_limit, index)
+                            + lighting * (1. - coef)
+                    },
+                )
+            }
+            Some(ReflTransEnum::Reflectivity { coef }) => {
+                self.reflection(point, coef, reflected, reflection_limit, diffraction_index)
+                    + lighting * (1. - coef)
+            }
+        }
+    }
+
+    fn refraction(
+        &self,
+        point: Point,
+        transparency: f32,
+        refracted: Vector,
+        reflection_limit: u32,
+        new_index: f32,
+    ) -> LinearColor {
+        if transparency > 1e-5 && reflection_limit > 0 {
+            let refraction_start = point + refracted * 0.001;
+            if let Some((t, obj)) = self.cast_ray(Ray::new(refraction_start, refracted)) {
+                let resulting_position = refraction_start + refracted * t;
+                let refracted = self.color_at(
+                    resulting_position,
+                    obj,
+                    refracted,
+                    reflection_limit - 1,
+                    new_index,
+                );
+                return refracted * transparency;
+            }
+        }
+        LinearColor::black()
     }
 
     fn reflection(
         &self,
         point: Point,
-        properties: &LightProperties,
+        reflectivity: f32,
         reflected: Vector,
         reflection_limit: u32,
+        diffraction_index: f32,
     ) -> LinearColor {
-        let reflectivity = properties.reflectivity;
+        // FIXME: use fresnel reflection too
         if reflectivity > 1e-5 && reflection_limit > 0 {
             let reflection_start = point + reflected * 0.001;
             if let Some((t, obj)) = self.cast_ray(Ray::new(reflection_start, reflected)) {
                 let resulting_position = reflection_start + reflected * t;
-                let color = self.color_at(resulting_position, obj, reflected, reflection_limit - 1);
+                let color = self.color_at(
+                    resulting_position,
+                    obj,
+                    reflected,
+                    reflection_limit - 1,
+                    diffraction_index,
+                );
                 return color * reflectivity;
             }
         };
@@ -208,6 +269,18 @@ fn reflected(incident: Vector, normal: Vector) -> Vector {
     incident - delt
 }
 
+fn refracted(incident: Vector, normal: Vector, n_1: f32, n_2: f32) -> Option<Vector> {
+    let cos = incident.dot(&normal);
+    let normal = if cos < 0. { normal } else { -normal };
+    let eta = n_1 / n_2;
+    let k = 1. - eta * eta * (1. - cos * cos);
+    if k < 0. {
+        None
+    } else {
+        Some(eta * incident + (eta * cos.abs() - f32::sqrt(k)) * normal)
+    }
+}
+
 #[derive(Debug, PartialEq, Deserialize)]
 struct SerializedScene {
     camera: Camera,
@@ -219,6 +292,8 @@ struct SerializedScene {
     aliasing_limit: u32,
     #[serde(default)]
     reflection_limit: u32,
+    #[serde(default = "crate::serialize::default_identity")]
+    starting_diffraction: f32,
 }
 
 impl From<SerializedScene> for Scene {
@@ -229,6 +304,7 @@ impl From<SerializedScene> for Scene {
             scene.objects,
             scene.aliasing_limit,
             scene.reflection_limit,
+            scene.starting_diffraction,
         )
     }
 }
diff --git a/src/serialize/coefficient.rs b/src/serialize/coefficient.rs
index e69de29..1b37875 100644
--- a/src/serialize/coefficient.rs
+++ b/src/serialize/coefficient.rs
@@ -0,0 +1,3 @@
+pub fn default_identity() -> f32 {
+    1.
+}