What is an Alum Block? (How To Use for Shaving & Where To Find)

Wet shavers are always looking for accessories that can take the shaving experience to the next level. Have you tried an alum block?

An alum block is a solid, rectangular bar of potassium alum that may be used as part of a shaving routine in place of aftershave because of its astringent and antiseptic properties. When used after a shave, it can help prevent razor burn and skin irritation, although it can lead to excessive dryness when used on sensitive skin.

Keep reading to learn what makes up an alum block, how to use one, and where to find one. 

What is an alum block?

Shaving often comes with nicks, cuts, and some skin irritation. Aftershave products can help minimize these effects. 

An alum block has both astringent and antiseptic properties. When used after a shave, it helps to prevent razor burn and skin irritation during the shaving process. It is also useful to stop bleeding and heal those minor cuts that are sometimes inevitable.

Alum in block form is very common, but you can also find it in a solid stick form as well. The stick form is commonly used for a deodorant, but it can give your face the same protection as the block form.

What is an alum block made of?

Alum can come in a variety of forms like powder, liquid, and solid. This compound is used in baking, water purification, leather tanning, and skin healing. 

An alum block is made of potassium aluminum, sometimes called potash alum. It is a double sulfate of aluminum and potassium. This solid block resembles white or clear crystals. 

Alum occurs naturally as the minerals alunite and kalinite. These minerals can be found in mines close to volcanoes or desert areas. Alum mines are commonly located in the Middle East and around the Greek Islands. Once these minerals are purified, you have potassium alum. It can also be formed synthetically by combining the two compounds, aluminum sulfate and potassium sulfate, in an aqueous mixture. Once the liquid evaporates, potassium alum crystals emerge. 

Alum was once the subject of industrial espionage. In 1491, alum mines were found in Rome. Thanks to Pope Nicholas V, alum mining soon became a secret papal monopoly. An English estate owner visited Rome and the alum quarries. The rocks looked similar to those he had seen on his own estate. Legend says he convinced some of the Pope’s alum workers to defect, so they could help him produce alum in England. When the Pope heard of his deception, he cursed the Englishman’s family and any future descendants or business ventures.

What makes an alum block work?

Alum has been used for centuries. In the ancient world, alum was often used for deodorant. The Romans used alum in their toga dyeing process because it helped the color attach to the fabric. Alum was also used in China’s paper-making industry.

An alum block’s astringent properties help tighten pores and aid in the coagulation of blood due to minor cuts. The antiseptic properties of alum soothe the skin and eliminate post-razor irritation, bacteria, and redness.

Alum is also used to treat acne. If you are plagued with breakouts, this small block can work double duty for you. According to a study in the Journal of Clinical and Health Sciences, potassium alum was able to kill four standard types of skin bacteria.

Can you use an alum block every day?

How often you shave will determine how often you want to use your alum block.

An alum block is safe to use every day, however, the block’s astringent nature can be drying to sensitive skin. If excessive dryness does occur, you can always follow up the alum step with a good moisturizer. 

Because of the salts contained in alum, you may feel a burning or stinging sensation after use if you have any micro-cuts in the skin. This is a normal reaction. In fact, many double-edge razor users take the intensity of the burn as a sign they need to adjust their shaving technique.

Rinsing the skin after a few minutes can eliminate any residual alum if this effect is especially bothersome to you.

How to use an alum block for shaving

You already have your favorite shaving routine in place.

Let’s discuss how to add an alum block to your process:

  1. Shave your face as you normally would, rinse well with cool water, and towel dry.
  2. Wet your alum block with cold water. Do not use warm or hot water because it will cause the block to deteriorate faster.
  3. Rub the wet block over your face, making sure to cover the area shaved.
  4. Leave the clear alum on your face for a cooling finishing step.
  5. If you experience dryness or your skin feels overly tight, you can rinse off the alum residue after a minute and follow up with a lotion. This step is optional and it’s fine to leave the residue on your skin as long as you don’t experience excessive dryness.

How long do alum blocks last?

Alum blocks are available in many different sizes with the most common being about 2.5-3 ounces. Some blocks are cut from a larger solid block, while others are molded from compressed alum particles. These differences in features can affect how long the block will last.

On average, you can expect a 3 oz bar to last a year or more with daily use. The block’s life span will be largely determined by the care and storage of the block. Warm or hot water will cause the bar to deteriorate more quickly.

Some bars will include a plastic storage case. If not, you will want to find one to protect your block. If you drop it, it will break. The pieces would still be useable but not very comfortable going across the skin

You want to minimize the amount of block surface area that makes contact with a counter or shower. While drying your block, prop it on your open case or turn it on its end. This will allow the block to dry more evenly.

As your bar dries, water can evaporate more quickly in some places than others causing a rough surface. If this happens, you can smooth it out easily with cool water. Alum blocks are very forgiving.

Is alum better than aftershave?

Different shavers have different habits and preferences. A 2017 study found that 29% of men aged 30-59 used an aftershave product every day.

Alum can be used as an aftershave product and can be the final step in your shaving routine. Many shavers prefer alum over other aftershave products because it is a natural product with minimal ingredients.

Alum blocks provide the cooling and toning effect often desired in an aftershave without any added perfumes or fragrances.

Where to buy an alum block

You’ve learned the benefits of using an alum block, so now let’s discuss where to find one. Surprisingly, they aren’t readily available in most chain drug stores or grocery stores. Some of these stores carry the alum block’s cousin, the styptic pencil. A styptic pencil is made from powdered alum and is used to stop bleeding.

The best places to find a wide variety of alum block brands are Amazon, eBay, and Walmart. These retailers offer a vast range of products and price points. Alum blocks can run between $4-70. Specialty grooming shops both locally and online are another option, however, their supply is often limited to one or two brand lines.

 Alum blocks can be purchased individually or in multiples for greater discounts.


Amazon offers an alum block to fit any budget.

Prices range from $5.98 for a 2.64 oz Planet 007 block to a whopping $62.95 Brianna brand stone.

The highly-rated French OSMA block is sold in a 2 pack for just under $12. Consumers like this brand because the OSMA blocks are cut from a larger solid block. They rate them high on smoothness and longevity.


The eBay auction site offers many choices available to “buy-now.” Pay special attention to shipping charges as some can be excessive.

The popular Parker Safety Razor brand block is available with free 4-day shipping at a cost of $11.99 for 4.4 oz. Consumers like the larger block size and the included plastic carrying case.


Walmart sells a wide range of brands and price points as well.

You can purchase a 3 pack of 2.82 oz GBS blocks for just under $10.

The classic shaving brand Taylor of Old Bond Street is available for around $15. Consumers say these blocks are soothing and refreshing.

Specialty grooming stores

A quick Google search brings up an array of specialty grooming stores both locally and online.

Popular online retailers like The Simple Man, Grooming Lounge, and New England Shaving Company offer a nice selection of alum blocks from the brands mentioned above plus more. Many of these stores offer discounts and subscribe-and-save options for all of your shaving needs.

Adding an alum block to your shaving routine can heal and improve your post-shave skin with minimal fuss and expense.

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