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Dear Arrighi,
When erasing lines I seem to smear my gouache. I thought gouache had a binder in it. Why does it smear and what can I do about it?
Signed,
Bindless
Dear Bindless,
Designer's gouache is made from many diferent ingredients one of them being gum arabic. Gum arabic is the gummy exudate from an acacia tree. It is used as an emulsifier in many food products and an adhesive or binder in inks, gouache, and watercolors. Gum arabic is water soluble and can be reconstituted.
Many artists put the gouache into a palette and leave it do dry then reconstitute it to work with. This gives some of the glycerine time to evaporate and keeps it from being "gummy". Designer's gouache is usually used to paint with and has enough gum arabic for that purpose and isn't necessarily meant for a rubber eraser scrubbing at it.
It's very helpful to try the color you want to use on the paper you plan to use and wait for it to dry and then erase carefully over it.
If it smears then you should add one drop of gum arabic. I wouldn't just routinely add a drop to every color unless you need it. Too much will make it gummy and when it dries the gouache will have hairlined cracks in it. Be careful when you are erasing, don't scrub the lines off, but gently coax them off with small strokes between letters.
Get into the habit of this and it will save a lot of work trying to fix smears and wrinkles. The binder will be different for various colors and papers. What works well on one paper may smear on another. It's always a good idea to do your prepatory work for any worthwhile project. It's saves times in the long run and keeps from having to recover from unforseen problems.
Signed,
Arrighi