A recent question mentions:
Bases are soapy to touch because of soap formation on contact with lipids present on our skin.
This is always the reasoning I hear, as well, and searching the internet gave the same results. However, when working with nitrile gloves, glass with aqueous sodium or potassium hydroxide on the outside always feels slippery. I believe that even nitrile-on-nitrile (rubbing the fingers together) gives the same slippery feeling. This effect is even stronger for the liquid in the base bath, but I assume that's because alkoxides would be detergents similarly to soap molecules in the absence of water.
Point is, if saponification is the culprit, why does the exterior of the glove experience a similar soapy effect to that my fingers feel? Could it be negative charges on the exterior of the glass? Is it possible for hydroxide to react with nitrile gloves to cause some similar kind of electrostatic repulsion, maybe by deprotonation or nucleophilic attack of the nitrile? This seems like a reasonable idea as far as glass goes, but I don't think that reasoning crosses over to gloves. Of course, I am not sure it really happens with glove-on-glove contact. I will safely test that theory again and edit if it's incorrect.
Answer
Glass itself is soluble in strong alkalis, forming sodium silicate solution, which is a syrupy, somewhat slippery-feeling substance. You can use sodium silicate to make a fire-resistant coating or high-temperature cement.
As you state, it's also possible the glove itself is being attacked. If the glass feels slippery in $\ce{NaOH}$ and $\ce{KOH}$ solutions, but not in $\ce{NH4OH}$, then it is most likely a silicate forming, though.
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