Clear Microsoft Ink

I have a windows form application which let an user to write in a picture box using Microsoft ink.

I have used below code to use the ink.


private void Form1_Load(object sender, EventArgs e)
{
  ink = new InkCollector(pictureBox1);
  ink.Enabled = true;
  ink.AutoRedraw = true;
} 
My problem is, I want to clear this ink when I click a clear button. Can anyone help me to do this?
Thank you.