Help with adding thickness to back face Meshmixer

[Anonymous]

I have a museum scan of a fossil fish that I would like to print out, however the scan has excellent detail on the upper surface but is extremely thin. It's not printable as-is right now. I need to somehow add thickness to the backside of the model without affecting the detail on the front/visible side of the model. I can create faces and the like, but it seems to only allow me to affect/modify the part of the scan/model that is depicted as grey-colored. The pink-colored backside of the model I'm unable to select or otherwise modify. Ideally, I'd like to add about 1cm to the back of the model for strength when joining all of the separate pieces together. It's a large fish so to print it on my two Prusa printers I need to divide it into roughly 16 pieces. I know how to break it down, I just have been completely unable to figure out how to add thickness to the backside of the model. 

[MagWeb]

Your mesh doesn't own any thickness. It is just a surface. The white side shows the front direction of the faces. The pink stripe pattern shows its back.

To add thickness (one of several ways):

1. Hit CTRL+A (CMD+A on Mac) to SelectAll

2. Run Select/Edit/Extrude on that selection. If you want to get a flat bottom set EndType to Flat and adjust Offset to a negative value (zero means an averaged plane based on the existing faces)

[Anonymous]

Thank you for the solution. I was able to figure out that by simply adding some positive value to the extrusion command after selecting was able to give some thickness to the model. However, that gave thickness that allows for printing but leaves a non-flat topology to what is the back side of the model. I'll try your suggestion today to see if I am able to achieve a flat back. Thanks again!