#define ORANGE     color(1,0.5,0.1)
#define WHITEMOULD color(1,1,1)
#define GREENMOULD color(0.3,0.4,0.3)

surface orange(float Ka=1,Kd=1,Ks=1;
                  float roughness=0.1;
                  color specularcolor = color(1,1,1);
                  float age=0.5)
{
  point Nf,PP,DP;
  point V=normalize(-I);
  float d,ks,kd,a,m;
  color cm; /* color of mould */
  float om; /* opacity of mould */
  color cs;

  PP=transform("shader",P);
  /* Make dimples on surface */
  d=abs(noise(30*PP));
  d=pow(d,6); /* make surface mostly flat */
  /* d=sin(0.5*3.14*d); round them off */
  DP=P-0.1*d*N;

  /* Put the end in slightly */
  DP=DP-0.2*pow(1-smoothstep(0,0.2,t),3)*N;
  DP=DP-0.2*pow(smoothstep(0.8,1,t),3)*N;

  /* Do some aging - make it mouldy */

  /* Make some duller sections */
  a=0.8*noise(1*PP)+0.6*noise(2.7*PP)+0.4*noise(5.05*PP);
  a=1-(1-a)*age;
  ks=pow(a,3)*Ks;
  kd=pow(a,2)*Kd;

  /* add some mould ! */
  m=4*noise(3*PP)*noise(6.7*PP)*noise(12.05*PP);
  m+=0.35*(age+age*0.5*noise(3*PP));
  m=m*smoothstep(0.3,0.6,age);
  m=pow(clamp(m,0,1),3-age*2);
  cm=mix(WHITEMOULD,GREENMOULD,smoothstep(0.5,0.8,m));
  om=smoothstep(0.4,0.7,m);

  /* combine underlying surface colour and mould colour */
  cs=mix(ORANGE,cm,om);
  ks=ks*(1-om);

  kd=mix(0.2,kd,smoothstep(0.01,0.02,t));

  Nf=calculatenormal(DP);
  Nf=faceforward(normalize(Nf),I);
  Oi=Os;
  Ci=Os*(cs*(Ka*ambient()+kd*diffuse(Nf))+
     specularcolor*ks*specular(Nf,V,roughness));
}