Hi, I want to make a cake and I need some gumpaste but do not want to make a new patch. I have some fondant left over from my last cake and am thinking of adding gum arabic to it . Will it work?

I too have wondered the same thing. When exactly is gum arabic used?

Hi, you can add tylose to your fondant to make gumpaste.  Take a look at http://satinice.com/how.php   under Betty Van Norstrand video «fondant to gumpaste».
 

One small correction.  Adding tylose to fondant does not make gumpaste BUT makes your fondant into something like gumpaste. It seems that you can't do this with a chocolate base fondant.

Adding gum arabic will not make it harder.  According to LorAnn Oils it is used to make gumpaste.  Here is the link.

https://www.lorannoils.com/p-8255-acacia-powder-gum-arabic.aspx