Determine if stuff is Potassium Alum How can one determine (at home) if the product shown below is Potassium Alum? I held a piece of it in a gas flame (assuming that the flame would become violet if potassium were present), but there was no change in the color of the flame. [Got product for use as astringent and antiseptic after-shave -- and people say (do not know why) that for such use, it has to be potassium-(not something else)-alum.]

Update: As mentioned in the comments to the chosen answer (by @James Gaidis), the product is ammonia alum. Just to be double sure, I repeated the tests with McCormick's Alum powder whose ingredient is potassium alum. (1) The picture of the flame test is below.

(2) With the McCormick Alum, the test involving sodium bicarbonate resulted in sound and definitely no ammonia gas.  (3) The solution of Fatkari had a salty taste that became sour in a second or so; the K-alum was tasteless and became sour in a second or so.
From Wikipedia:

An alum is a type of chemical compound, usually a hydrated double sulfate salt of aluminum with the general formula $\ce{XAl(SO4)2 · 12 H2O},$ where $\ce{X}$ is a monovalent cation such as potassium or ammonium.

There are also chromium alums and ferric alums, but the color in your sample does not seem to suggest either of them.
The alums melt at relatively low temperatures, because they already have a lot of water in the crystal structure, so ammonium alum and potassium alum can not be differentiated on the basis of melting points. Solubilities are fairly close, too:
$$
\begin{array}{llc}
\hline
\text{Compound} &amp; \text{mp}/\pu{°C} &amp; \text{Solubility}/\% \\
\hline
\ce{(NH4)Al(SO4)2 · 12 H2O} &amp; 93 &amp; 15 \\
\ce{KAl(SO4)2 · 12 H2O} &amp; 92.5 &amp; 11 \\
\hline
\end{array}
$$
If there is no violet color to a flame, there may be no potassium, but the test can be sensitive and may be indeterminate. Eliminate the possibility that the alum is an ammonium salt by dissolving some in water and adding a strong alkali, then sniffing it gently. If you smell ammonia, you have an ammonia alum; it will still work as a flocculant for muddy water, but is different chemically. A strong alkali readily available at home, well, at the grocery store anyway, is sodium carbonate (washing soda).