This page was created from Joel's Interactive Guide to Straight Razor Shaving and can be discussed in this thread[1].

I decided to make this page to teach people how I assess the edge quality at the most important step in the honing process, the bevel creation stage. If you learn to use these tests well and together, then I am confident that the quality of your edges will improve, and it will take you a lot less time and experimentation/guessing to get a great shaving razor. As far as I am concerned there are only two main types of tests: edge thickness (sharpness) test and edge uniformity tests. Both are equally important and have their own strengths; however, both have their weaknesses as well. Therefore, they must be used together to produce the highest quality and most consistent edges in the least amount of time.

These are the tests that you probably hear a lot about: the thumbnail test (TNT), thumbpad test (TPT), and of course the famous hanging hair test (HHT) and its many variations (arm hair, badger hair, etc.). I am not going to go into detail on how to perform these tests because there are already many great threads from experienced members explaining how to perform these (at least over at the SRP), just use the search function and you will get as much information as you could ever want. I will give you a summary of how to perform each of the tests and then explain their strengths and limitations individually and as a whole (which are addressed with the edge uniformity tests).

The thumbnail test is performed by dragging the edge of the razor (from heal to toe) along your wet thumbnail. The feeling that you want is for the razor to have a smooth and even bite indicating that the bevel is sharp enough to cut into your nail. If the edge glides across your thumb nail easily without resistance then it means that the edge is too dull to bite into the nail and will need more work to get sharp. If you feel the edge bite in but it feels "rough" in certain areas then this indicates that there is roughness such as microchiping or overhoning in that portion of the edge that will need to be worked out before moving on to the polishing grits. Do not perform this test past the 4K stage because the edge will be damaged.

I perform the TPT by lightly pressing and dragging my wet thumb along (not across) a small portion of the edge. The feeling that I am looking for is a smooth sticky feeling caused by the edge slicing into my skin. I then lift my thumb off that portion of the edge and check the next portion in the same way going all the way from the heal to the toe. You will likely find that some areas are sharp and some others are not, indicating that blade will require more work to get uniform sharpness from heal to toe.

There are several different variations of the HHT. The standard test is to hold a hanging hair between your thumb and index finger and then bring it to your razors edge. The hair should be easily and cleanly cut in two pieces (not peeled down the center). The HHT should be performed along the entire blade from heal to toe in order to make sure that the entire edge is sharp. Another variation of the test (which I do not like as much) is to bring the edge across your arm hair and assess how easily it pops the hairs. In my opinion the major shortcoming of this test is the fact that it will not tell you which portions of the blade are actually very sharp and which are not because hairs will be popping all over; it gives you more of an idea of the average level of sharpness of your entire edge. If you are a perfectionist like me you will want the entire edge to be at its optimal level of sharpness. Another variation of this test is to pick one particular hair on your arm, and attempt to cut it with a particular portion of the edge. Different hairs can sometimes react somewhat differently in the HHT, and the general rule is the thinner the hair the sharper your edge will need to be to cut it cleanly.

All of these tests are fundamentally testing the same thing: the thickness of the edge (not width of the bevel) which is more or less the same as the sharpness. Many people say that the only real test is the shave test; however, I have NEVER had a great shaving razor that did not at least pass these sharpness tests very well. In fact I would go so far as to say that passing these tests well is a pre-condition to having a high quality edge; if your razor will not pass the sharpness tests and you think that you are getting good shaves then all I can say is that you don't know what you are missing because you are getting a great shave in spite of the edge; not because of it. Take the time effort to learn what these tests should feel like and correlate the results to your shaves and the quality and consistency of your edges will improve and it will take you a lot less test shaving to get there. If you can run your thumb along the edge without it cutting in, run the edge across a wet thumbnail with no drag, and/or the blade will not pop hairs suspended above your skin then I can guarantee that your blade is not sharp enough at this point and that you have at least a fair amount of work left to do on the 4K (or other bevel creation stone) if you want to finish with a quality edge.

These tests are more subjective than the Edge Uniformity Tests which I will explain in the next section; however there is definitely a proper way to perform the tests and a right and wrong way to interpret the results. The tests are not a pass fail thing, sharpness is more of a continuum or scale. What one person may perceive as a very sharp edge, another who is more experienced may perceive the same edge as dull based on the results and their experience using the tests. Personally, I think that I can get a lot more information about the thickness/sharpness of an edge by the results of the TPT or HHT than I can from the TNT; furthermore I think that there is a higher possibility for damaging an edge with a thumbnail so I stick with the thumbpad and HHT. It takes time and experimenting to interpret the information that these tests give, and someone with more experience will definitely be able to use these more effectively than someone just starting out; however, this does not mean that these tests should be ignored.

The main limitation with the sharpness tests is that they cannot detect a double bevel in the edge or even the places where the stone is not contacting the edge if that portion of the blade was already sharp (at a steeper angle); the edge uniformity tests are needed to detect this. In my experience, the most common times when this common problem shows up are when you are honing a factory sharpened razor for the first time, and when you establish a bevel with tape on the razor to protect the spine from the dreaded hone wear during the early stages and then try to finish honing the razor with the tape off the spine. Basically the problem of double bevels arise whenever a sharp bevel was set at one angle (steeper) and you are trying to hone the razor at another angle (shallower) When you perform the sharpness tests on the razors they will appear sharp as indicated by the sharpness tests, and they are indeed sharp at the 4K level. The problem is that when you try to improve the razor with the higher grit stones you will be doing absolutely nothing to the edge of the edge. The angle that the bevel and edge is set at is at one steeper angle (caused by the factory sharpening the razor with the spine lifted to avoid selling a razor with hone wear, or you setting the bevel on a razor with tape to protect the spine and then removing it for further polishing), and you are honing the razor at a shallower angle because the spine is now on the stone and only the back of the bevel is in contact with the stones. This means that the rough but fairly sharp factory edge or 4K edge will remain regardless of the amount of touch-ups or fine tuning that you do with the finishing stones because the edge that you are actually shaving with has never been in contact with the higher polishing grits. The razor will shave the same and you are absolutely wasting your time until you establish a uniform bevel. At this point I hope that you are asking yourself, How do I know when I have established a single uniform bevel? Great question! The answer is that you assess this by using the Edge Uniformity Tests which are explained in the next section.

The edge uniformity tests are just as important as the edge sharpness tests because they address the important issues that the sharpness tests do not; however, they are unfortunately overlooked many times leaving people with sup-par edges that will not get any better (or worse) with any touch ups or fine tuning. There are only a few edge uniformity tests that I am aware of, and I have found that the easiest and most effective are the permanent marker test and the microscope test. The microscope can also be used to assess other problems such as micro-chipping and overhoned edges; however, it is not really talked about much in terms of assessing edge uniformity as I am going to explain now. The permanent marker test is a very easy test to perform and interpret; it is a pass fail thing. All that I do is mark the edge of the bevel with dots that go to the very edge of the edge all the way from heal to toe (yes you can use a line too if you want). Then when you hone the razor the marker should be completely removed with a few passes indicating that bevel is completely uniform and the stone is contacting it everywhere and all the way to the edge. If your razor passes this test and also passed the sharpness tests very well then you can be confident that you are ready to move on to the polishing stages, and you will have a razor that shaves great when you are done. On the other hand, it is very likely that the dots will not be completely removed, and you will know that your edge is not uniform and will not be sharpened any further with the higher grit stones. If the dots or line is removed toward the back of the bevel but marker remains at the edge of the edge then you have the very common and significant problem of a double bevel. You must hone on the 4K (or courser stone) until the marker is completely removed all the way to the very edge so that you know that the double bevel is removed. This will allow the fine stones to work their magic on the cutting edge and give you a very sharp, smooth, and great shaving edge.

You can also perform a very similar test with the microscope as I learned from Mr. Randy Tuttle. You will be able to see a double bevel in your edge if the edge is two different colors and has two different scratch patterns. The difference is because the light will reflect differently because of the slight difference in the angle, and the scratch pattern will be different because it will not be from the stone that you are currently working on, it is from the stone that set the first bevel angle. When you are done removing the double bevel, the bevel should only be one color (black) and should have only one scratch pattern from the stone that you are currently using that extends all the way to the very edge. You can also use these two edge uniformity tests together to ensure the best results.

These tests allow you to see if the entire edge is contacting the hone, or if you have issues such as a double bevel that need to be worked out. If you attempt to use finishing stones when the edge of the edge is not contacting the hone as in the case of a double bevel then you will be doing nothing but wasting your time because the edge of the razor won't see them. If you only have one even bevel then at least you know that the stone is working on the most important part of the bevel; the edge.

You cannot see the bevel thickness or sharpness with a microscope or the magic marker test, all you can see is how the side of the bevel is contacting the hone. You could have the prettiest, shiniest, and most even side of the bevel; however, that absolutely does not mean that the edge is sharp. You must use the sharpness tests to determine if the bevel actually meets at an edge.

I hope that after reading this short guide you have a better understanding of both the strengths and weaknesses of the two main types of tests and how to use them to assess the edge of a razor, especially during the very important bevel creation stage. The TPT, TNT, and HHT will tell you if your bevel is sharp but not uniform, and the marker test and/or the microscope will let you see if you have an edge that is contacting the stone uniformly and hopefully all the way to the edge, but it will not tell you the thickness/sharpness of the bevel. Both tests have their strengths and weaknesses, so the results are best when they are used together. Unfortunately we cannot see everything that is happening at the microscopic level of our razors edge; however, by using these various tests together we can give ourselves a very good idea of what is going on at the edge level. After a quality bevel as indicated by the tests is both sharp AND even then you just need to polish it carefully with your method of choice, strop it up, shave, and then fine tune it a little if you feel that it is necessary. If you like to use Belgian stones then I have found that using 50-100 passes on both the blue and yellow produces consistently superior results, as does a few light pyramids on the Norton 4K/8K (or even just a few passes on the 8K). Hopefully these tests can take some of the guess work out of the honing process for you, because whiskers only grow so fast.