Subject: Why do phenolphthalein agar cubes turn white on the edges in NaOH?

Thanks for getting back to me on this question!  The outside edges on the 
cubes turned pink and then white the longer they were imersed in NaOH.  The 
entire cube was submerged in the solution.  When put into the solution, the 
edges of the cubes immediately turned pink and the longer they were left 
in, the farther the pink color traveled.  However, after a while, the 
outside edges turned back to white, (the middle was still pink)  It could 
be that the phenolphthalein dissipated.  Hope this clears it up.  Again, 
thanks for all your time. 

Re: Why do phenolphthalein agar cubes turn white on the edges in NaOH?