If you want to know the very good reasons ( you do ),
for those two sizes, take my "materials" lesson on WATERCOLOR PAPER.
If you are uncomfortable painting any of my lessons because of limited drawing skills, please use my drawing skill. All of the paintings demonstrated on this site come with drawing templates to help you transfer my drawing to your paper.
This short, 4 minute video will show you how to make a beautiful painting with no drawing skills whatsoever.
If you are somewhat comfortable with drawing, its easy to personalize my drawing, to make it yours.
If my lines are not straight enough, or my angles are not square enough for you ( It;s OK if they are not ), just use a straightedge to clean them up.
Just below the double line there are 5 links/buttons. Fourth from the left says "Get The Drawing Template" or "The Coloring Book". Hold your mouse over it. More links should appear just to the right. The template you want should be among tem. Click it.
A new window should open with your template in it. There should be a horizontal menu bar just above the picture of the template. The first icon on the left should be a printer. Click it and follow the print instructions; which probably include "Print".
The template is in a file made for Adobe Acrobat. Just about every computer comes with Acrobat. If you need it, you can download it at:
Copy the above line and paste it into the address bar of your browser. Adobe has the download button at the lower left on the page.
The map shows the location of each of the paints. The group on the left are the sedimentary colors. Those in the right are the non sedimentary colors. The palette is just a cut down ice cube tray.
...( sedimentary )
0 - Red
1 - Yellow
2 - Green
3 - Blue
...( non sed. )
4 - Cool Blue
5 - Warm Blue
6 - Warm Red
7 - Cool Red
8 - Warm Yellow
9 - Cool Yellow