How Does Vinegar Bind Clay?

To create a join in your clay construction that is stronger than water or slip alone – try using white vinegar. Since clay is slightly alkaline, the acidity of vinegar makes it act like a glue for clay. Apply it to both surfaces and press the pieces directly together without slipping or scoring. The acidity of the vinegar breaks down the clay a bit, and makes it sticky. Some artists use vinegar straight from the bottle, or add vinegar to clay (instead of water) to make a joining slip. You will find the vinegar in the studio on the shelf near the sink area. Magic in a bottle!

And now for a very technical answer:

Vinegar is used in clay bodies to increase acidity to improve plasticity. The acid works to neutralize sodium ions (from water, leaching feldspars) that tend to deflocculate the clay. However, excessive acid may tend to dissolve more feldspar or nepheline syenite negating the effect.

(A-ha, now I only need to know what deflocculate means – Editor)