No, I'm not making this up as this method actually works as it can really put that razor sharp edge on your straight razor! Honing a straight razor using glass is a method that is seldom used, even for traditional straight razor users as this technique is used specifically as an alternative to leather stropping. The methods used in this particular honing technique require the use of any glass surface, such as an old mirror or a discarded glass panel that can accommodate the entire length of your straight razor. The smooth surface of the glass should be roughened out with the use of any 200 to 250 grit sand paper as this will provide just the right amount of abrasiveness to perfectly grind off any excess metallic materials from your razor's blade.
You need to make sure that the entire surface of the glass is roughened out so that it will be able to cover the entire area of the razor's edge. Washing the freshly rubbed glass, you can then add a few drops of any kind of light lubricating oil and spread it on the glass surface. To make it very clear, this method is only used on a straight razor that has been previously been honed and used and this method can not sharpen a straight razor as efficiently as a whetstone. Unfortunately, using a whetstone can sharpen your straight razor, but using it the wrong way can leave "nicks" on its blade, dulling out the blade instead of sharpening it properly.
This is the most difficult thing that could happen to your straight razor. Recovering the blade's original sharpness is very hard if prior honing has left it much worse than it is. Glass honing can recover the original sharpness of you blade, though it would take twice the time compared to using a whetstone. But the best part of this method is that honing your straight razor on glass will not leave nicks on your blade since the glass surface of the panel that you are rubbing your straight razor is almost perfect, giving it an even edge.
Most of the time, the use of chromium paste or honing paste is used to quicken the honing process since chromium paste contains finely grounded metallic particles that help in grinding out the razor's blade. In the case of glass honing, cigarette ash, paper ash and charcoal cinder can be used as an alternative to honing paste, which is finer than the metallic particles in chromium paste. This is done by applying a few drops of light lubricating oil on the glass and rubbing on some ashes on the glass. This will act as an abrasive that will sharpen and polish the razor's edge.
Unlike honing using a whetstone, glass honing requires no definite pattern when running the straight razor on the glass surface, though the most commonly used method is making circular motions on both sides of the razor's blade without having to worry of evenly giving the razor the right amount of sharpness. Since the mixture of the oil and ashes will begin to grind off any and unevenly metallic particle from your razor blade, you will notice that the blade will begin to produce a sticky sensation as you continue rubbing it against the glass panel.
Determining if your razor has already reached a certain point of its optimized sharpness, you will begin to hear a swishing sound similar to that of a scissor. This tells you that the entire blade surface is now perfectly grounded off and it is now as evenly as the glass surface. You can verify this by performing the hanging hair test in which you can try to cut off a piece of hair by simply dropping it across the blade to see if it can cut it. However, the density of human hair differs from thickness as facial hair is much harder to cut off and passing the hanging hair can not prove that your straight razor is indeed sharp enough.
You can try to shave off a certain segment of hair from your legs as these particular type of hair closely resembles hair on your face. As always, remember to wash off any remaining dirt and grime from your straight razor and let it dry out along with applying a generous amount of light oil to prevent oxidation. Rust build-up is very common on carbon steel razors since its metallic property is prone to this. Oil gives it a protective coating so that you can store it until such time that you will use it again. Always remember to take care of your straight razor so that it can give you many years of enjoyable shaving experience that can last a lifetime!
