Why can't I change the value of ImageTransparency?

I was trying to see how a particular image would look if it were to fade in/out.

a = game.Workspace.Part.SurfaceGui.Frame.ImageLabel.ImageTransparency

for i = 1,10 do
     a = a - 0.1
     wait(0.04)
end

For some reason, it doesn't change the value at all. When I made the script print the value of "a," the number did decrease, but for whatever reason, the gui remained unaffected.

When defining variables, do not set them to an object's property.

a will become whatever the ImageTransparency is equal to at the time it was created. a is in no way connected to the ImageTransparency property. It it simply a number, the same as a = 1 or a = 2

Set your variables to objects, not their properties.