Difference Between STRAW MARK and CRACK in Glass -- Help Please

[sophies*finds]

Hello, everyone.  I have an old Jeanette Glass Windsor bowl that has two lines on the bottom.  Wondering how I can tell if they are cracks or straw lines.  They don't go through to the inside of the bowl, but I can feel them.  Any help is much appreciated.  Thank you.

[gabla]

A photo would help. A shear mark aka straw mark is caused when the shears used to cut a glob of molten glass from a gather so it goes into the mold cools the glass faster causing either a ridge or a valley which does not go through the glass. A fracture aka crack will go through to the other side and by rotating the item you often can see the sides of the fracture. An item may hold together for a long time with a fracture.

[sophies*finds]

Good morning, George.  Thanks so much for your kind and informative input.

I had some old Madrid plates with straw marks that I couldn't feel, which led me to believe the lines on this piece were cracks.  Here's a rather poor picture that I hope will help.

[gabla]

Sure look like shear marks to me.

[sophies*finds]

Thank you again, George.  The more I stare at them, the more they look like shear marks to me, too.  I think I'm correct that Jeanette pieces are often flawed with shear lines and bubbles in the glass.

[sophies*finds]

Jeepers!  Will I ever remember the extra "N" in JeanNette???

[msgood2shoe]

Jeannette and other low cost manufacturers were more concerned with quantity vs the quality of the pieces, so slight imperfections weren't cause for the item to be pulled and not sold.