What is an alum block?
The humble alum block is the unsung hero of classic wet shaving. Alum is a natural, crystalline stone that has been in use for thousands of years for its healing properties, as it is both astringent and antiseptic. More technically, it is a naturally occurring chemical compound called potassium aluminium sulfate, which is a double sulfate of potassium and aluminium. Also known as just potassium alum or potash alum.
The best alum blocks are made from a single piece of potassium alum that’s been shaped and polished ready for use.
An alum block can also be referred to as an alum stone or an alum crystal.
What does an alum block do?
Alum is an astringent which causes the skin cells and tissues to shrink.
Used in shaving, it helps to soothe freshly shaved skin to combat razor burn, ingrown hairs, bumps, and redness by reducing inflammation. It’s also effective at stopping any bleeding from nicks and cuts by constricting the blood vessels.
Lastly, it tightens pores and acts as an antiseptic that kills any surface bacteria, which helps to disinfect freshly shaved skin and prevent infection and spots.
Outside of shaving, it has a number of practical applications that make use of these properties; such as in natural deodorant, in food, as part of leather tanning, in textiles, and in water purification.
But the true genius of an alum block is in technique monitoring, making it an essential tool when learning to shave using a double-edge (DE) or straight razor.
Even if you’ve had a comfortable shave without razor burn, there is likely still room to improve. Poor technique or blunt blades are often the cause of microscopic cuts and nicks that are invisible to the eye.
When you rub the alum block over any hidden spots of irritation it will immediately sting (the intensity of the stinging tells you how bad the irritation is). You can use this stinging to identify areas of your face where you are perhaps not being careful enough or it could be a signal that your blade needs changing.
The stinging feeling from applying alum to irritated skin only lasts a few seconds as it helps to soothe and reduce inflammation.
When you can consistently run an alum block over your freshly shaved skin without a hint of stinging, you know you have mastered your wet shaving technique!
What is alum made from and how is it made?
There are 2 different types of alum stone used in shaving: ammonia aluminium sulfate, which is lower quality as it tends to sting more; and potassium aluminium sulfate, also known as potash alum, which usually looks cleaner and is more comfortable for use on the skin.
Historically, as far back as 2000BC, alum was mined as a naturally occurring mineral. By the 13th century it was being manufactured in Europe by burning vast quantities of rock until only a white powder was left. This was then passed through water before ammonia was added to separate out the iron sulfate. Pure ammonia aluminium sulfate crystals would then form and could be collected.
Alum was important because it was required as a fixant for dying wool bright colours, essential for the textile industry.
Today, potassium alum is made industrially by adding potassium sulfate to a concentrated solution of aluminium sulfate.
What is a styptic pencil and how is it different from an alum block?
Although made from the same material, styptics and alum blocks differ slightly in how they’re made and when to use them.
A styptic pencil is typically made from alum that has been ground down into a powder and then reshaped into a stick for easy application. Because it has been powdered, a lot more comes off when applied to damp skin which makes it stronger. For this reason, styptics are used solely for when you cut yourself because the powder does a more effective job of tightening the area and stopping the bleeding.
A block on the other hand only imparts a small amount of alum when run across the skin so it just stings a little bit when coming into contact with areas that could be improved. This makes it ideal for running over the whole shaved area as it will last a lot longer whilst still doing the job of alerting you to where your technique needs some work.
How to use an alum block in your shaving routine
1. After you’ve finished shaving, rinse your face with cold water to close the pores.
2. Wet the alum block with water and then proceed to gently run it over your face and neck and any area where you have shaved.
3. If you go over a patch that stings, take note. Do you remember going over that spot with less care and attention? Try to remember for next time and see if you can alter your technique to be more gentle. This is how you continually improve.
If your whole face stings but you’re confident from experience that your technique wasn’t off, that is a likely sign that your blade needs replacing.
4. Leave on the skin for 30 seconds to give it time to do its job and soothe the skin (use this time to clean your shaving brush and put away your razor etc)
5. Rinse the alum off your skin with cold water. It’s important that you rinse it off otherwise it can be quite drying if left for too long.
6. Rinse the alum block and then leave in an open space to dry between uses. If you let it sit where water can pool, it will dissolve!
7. Continue your normal after shave routine to re-hydrate your skin such as applying a post-shave balm.
Where to get an alum block?
As part of our shaving club, we feature a natural alum block roughly once every 18 months (they're so long lasting). We also feature alum products in our shop.