The Heat Treatment Of Straight Razors In The 1800s

I am sure that we all have our own favourite old razor – it just feels better than the others and yet it is just a piece of sharp steel. I often ask myself why they all feel different. And so, I have written this article to consider how our old razors were given some of their individuality by the highly skilled razor smiths who made them.

These old razors were hand crafted usually by a man and an apprentice in a simple blacksmith’s forge using carefully guarded secret processes well before the age of science and technology that we now take for granted. This was a time when secret (almost magical) knowledge and skills were passed down from razor master to apprentice over many generations – the science of metallurgy didn’t exist, just hundreds or even thousands of years of practical experience.

I do not intend this to be a scientific explanation of the heat treatment processes of steel (there is much more detailed information on this available on the internet) but I do want to give an idea of how the early razor masters would have approached it. I will also avoid using technical names for the processes as there are often many names for the same thing and I don’t want to cause confusion.

In an earlier article I explained how the superb and very expensive steel for our razors was the product of a long series of very specialised refining processes that started with Swedish iron ore and ended up with small batches of high quality steel that varied from one iron master to another and even from batch to batch. Our razor smith would always buy his steel from a particular iron master because he trusted its properties and knew how to work with it.

The old razors were shaped from a bar of steel by hand – hammering, grinding and filing (long before hacksaws, electric grinding discs, laser cutters etc. were even thought of). To help him in his work our smith would use heating and cooling to produce the mechanical properties that he needed to work the blade. It was discovered thousands of years ago that heat treatment magically changed the mechanical properties of steel to make it easier to shape by hammering, or to relieve the internal stresses due to the hammering and finally to harden the blade so that it could take and keep a fine edge without making it brittle or prone to chipping.

There are two main heat treatment skills that our smith would have mastered during his apprenticeship: raising the blade to the correct temperature and then cooling it down again. That sounds straightforward enough but get either slightly wrong and the blade could be ruined by warping or even splitting. Not forgetting our smith could make perhaps two razors a day, and so a ruined one would cost him dearly.

When heating, our razor smith had to judge the working temperature by observing the colour changes of the metal when heated in his forge. The modern chart below shows us how the colour of heated steel varies with temperature – colour changes are very subtle and can happen extremely quickly and so careful control of the fire was vital. The desired colour would have been carefully judged (ever wondered why blacksmith’s forges were dimly lit). In general, higher temperatures for shaping and hardening and lower temperatures for stress relieving and softening. The exact temperature and rate of heating required would have varied from one batch of steel to another and so our smith would have needed all his acquired skills to get it just right.

So that is the heating part, now the cooling. Sounds simple but this is the real “make or break” stage – literally! Cooling can be anywhere between fast and slow depending on the properties required. In general, fast for hardening and slow for stress relieving.

Fast cooling involves submerging (or partially submerging) the very hot blade in a “coolant”. To achieve subtle changes in the blade’s properties the smith might even cool some parts of the blade differently – say to give a hard edge and softer more flexible spine. Hence, he would dip the edge in the coolant first and sometime later the rest of the blade.

Now the interesting part – the choice of “coolant” and again each smith would have his own (secret) recipe handed down from his master, and perhaps modified further to what works best with the actual steel that he has chosen to work with.

Traditionally, water, animal fats or fish oils were used, but here are some interesting old recipes that I’ve come across from around the world – honestly, I have not made them up:

“mix together 1 measure of Quick Lime, 1/2 measure of Soda, 1/2 measure of Carbonas Cupricus, 1/2 measure of Arsenic Sulphate, 2 measures of Radish juice, 1 measure of Wild Onion juice, 1/2 measure of Valonia ash and 1 measure of Tar”

“Clarified honey, fresh urine of a he-goat, alum, borax, olive oil, and salt; mix everything well together.”

“Urine of a small red headed boy”

“Take varnish, dragon’s blood, horn scrapings, half as much salt, juice made from earthworms, radish juice, tallow, and vervain and quench therein”.

These are quite bizarre, but there is a method in the madness, and that is to minimise the size of the bubbles that form as the coolant boils from the hot metal – large bubbles cause tiny differences in the cooling rate across the blade and hence change its properties from those desired.

Slow cooling involves allowing the hot blade to cool naturally in air. But even this can be modified – I have seen one account where a swordsmith cooled his blades by giving them to a horseman to “ride about very fast whilst waiving it violently”! Perhaps this was a bit of showmanship on the behalf of the swordsmith to give a sense of mystery and power to his blades.

Below is a chart showing the colours of steel at different temperatures – our smith would not be interested in actual temperature (as he had no means of measuring it) but he would have to know the colour that he was aiming for to achieve a particular change in the metal. As you can see the changes are quite subtle and the smith would have been very skilled in getting it just right.

So, I think that we can see that our razor smith had much to learn and perfect during his long apprenticeship and this knowledge and skill would stay with him for the rest of his working life. With all the variables mentioned above I think we can begin to realise just how individual each razor smith’s razors really are.

You might ask how has this all changed since the old times? Well, science now enables us to manufacture huge quantities of high-quality steel that is very uniform in nature and can be made specifically to suit a particular use. Modern instrumentation allows ovens to be set to exact temperatures and chemists have developed specific coolants for specific steels and even use liquified gases to super cool steels making them incredibly hard. Sadly, in the quest for progress all of this removes that unique character that our old smiths were able to give to their little works of art.