diff --git a/_subsections/chapter04.org b/_subsections/chapter04.org
index a1900a3..37ea734 100644
--- a/_subsections/chapter04.org
+++ b/_subsections/chapter04.org
@@ -127,6 +127,35 @@ the way to unlink  or unlink is to click on the link icon that connects the mask
 - =CMD+I= invert the mask
   - apply the smart filter mostly to the background
 
+** problem copying masks
+- can create a weird effect
+- instead group layers
+- apply mask to group
+
+*** to copy a mask
+- ALT + drag and drop
+
+** double masking
+but the masked layer into a group and give that a mask
+
+** using image as a mask
+- put a background color behind the image
+  this will be the color that goes through the mask
+- select the image
+- hit the  mask button
+- copy another image to the clipboard
+- select the mask part
+- hit OPT+click on the mask
+  - this opens up the mask for editing
+- paste the 2nd image into the mask area
+  - add black to anything you want to hide of the masked image
+- click anywhere outside of the mask on the layer panel
+
+*** to change highlights in mask
+- select mask
+- hit CMD+M
+- this brings up curves
+