You think marketing companies these days are pretty slick. This envelope from 1914, dug out of The Box of Old Stuff, features a picture of a one-pound can of Magic Baking Powder on the front, and on the back — now here’s the sneaky part — what appears to be a handwritten postscript from whoever sent you the letter.

It reads, “Forgot to say that we find Magic Baking Powder is O.K. It is different to most, as it does not contain Alum.” It’s printed on there, of course.

I was shaking my brain trying to recall what the hell was wrong with alum. Wikipedia tells me they used it in skin whiteners in Shakespeare’s time and as a hair stiffener in the 1950s, and it’s still used in hair-removing wax in the Middle East, as a deodorant in many parts of the world including Thailand (sahn-som!), to stop shaving cuts from bleeding, as a home remedy for pain and canker sores, for fireproofing paper and — here we go — in pickling veggies and keeping them crisp.

Another website says potassium aluminum sulfate, also known as potash alum, and sodium aluminum sulfate, which is the one in baking powder that gives a vague metallic taste, are approved by the US Food and Drug Administration as a food additive, but if you swallow an ounce or more it’s toxic, so its use is discouraged. And yet another site points the finger at calcium aluminum phosphate — “now being phased out, owing to current beliefs that aluminum may be bad for us at much lower levels than was previously known”.

Regardless of the enemy’s name, yet again, advertising saves lives.

Magic Baking Powder is the brand now owned by Kraft that’s made and sold in Canada, where the envelope originated, but by the time the EW Gillett Company started producing it in Toronto in 1897, commercial baking powder for quickly leavening batter had already been around for half a century.

Its invention is credited to Justus von Liebig in 1835, as a blend of baking soda, cream of tartar and starch and marketed as Royal Baking Powder. Eight years later British chemist Alfred Bird’s wife was allergic to eggs and yeast so he “improved” baking powder for her and ended up selling warehouses of the stuff to the army.

In the 1850s the cream of tartar was swapped for slower-acting calcium aluminum phosphate, and then in 1885, sodium aluminium sulphate was discovered, and it waited to react until the dough was actually in the oven. Calumet Baking Powder became America’s choice in 1889, but today the favourite there is the quaintly named Clabber Girl Baking Powder, a brand that’s also more than a century old.