Why does glue start white and then dries clear?

The smiley face on the top half of the image is wet glue– All white. Whereas on the bottom half of the image you can see it gradually turning clear in the thinner parts first, where the water is evaporating.

As a kid, arts and crafts were one of my favorite hobbies, and still is now. Most craft glue, Elmer’s brand especially, comes in a thick white color, and if you have never used glue before you would think it would dry the same color. BUT NO! Glue has properties in it that make it dry clear, so crafts and other projects don’t seem messy. This is great an all, but HOW does this color transformation¬†happen? Craft and school glue are essentially made of Polyvinyl acetate¬†(PVA), a powdery substance that doesn’t mix well with water, which turns into other stages, forming the hardened and fastened glue.

This glue dries colorless

A science blogger, “John The Math Guy” explains the breakdown of wet glue and why it forms to the clearer hard state to hold objects together. The reason glue looks milky, as he puts it, is because the PVA is mixed with water which causes it to be wet. Since the water is the part that is wet and therefore will dry, that causes the PVA to turn clear, since it has nothing keeping it wet anymore. The water evaporates, which leaves only PVA plastic leftover, which is clear.

So it isn’t as complicated as I thought- It just has to do with water evaporating and leaving behind the clear PVA particles.

3 thoughts on “Why does glue start white and then dries clear?

  1. Lucille Laubenstein

    In my opinion, glue has to catch phrases that originate in elementary school. They are “Just a dab will do ya”, and “Glue dries clear”! Both are catchy, and informative about glue, however the latter is more scientifically intriguing. The US Department of Energy provides further explanation on the subject. In this link https://stab-iitb.org/newton-mirror/askasci/chem07/chem07250.htm , a few scientists answer the same question. One, explains that glue is a colloid. A colloid, is when there are molecules of various sized homogeneously mixed within a second substance, like PVA in water. Other examples of colloids are mayonnaise, and milk.

  2. Kameron Villavicencio

    I was intrigued by the title of this blog. I was fascinated by what studies could have been done on glue. I think this blog could be improved by going into the science. Perhaps you could compare types of glue, or glue brands. This article http://www.adhesives.org/adhesives-sealants/adhesive-selection/types-of-glue-glue-tips, goes into different types of glue. Maybe studies have not been done, but although this is an intriguing topic, it lacks depth.

  3. Michael David Harding

    I was the messy arts and crafts person of my school. I hated art class because I would come home with that DAMN dry glue all over me. Although I never put too much time or energy into finding out why it dried clear, it is very interesting to know how simple some things are. To me that is what science is all about, discovering new things and feeling achieved when you figure out something difficult and to laugh and enjoy the simple things. Obscure, but interesting post.

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