Notes on natural stones

If you have not used a hard stone before here are a few other suggestions. Start your trials with a 1 1/2 or 2 inch chisel or a 65mm or 70mm plane iron. The extra width will allow the most contact between the stone and blade so that you do not have to focus on the bevel angle at first.
Another thing, and I have run into this before, remember the natural awasedo stones will leave the soft iron (jigane) and the hard steel (hagane) with a different polish that is in contrast to each other.
Most people are used to seeing the blade being all one polish on both the metals looking like a mirror after using synthetic stones. In Japan this contrast in polishes is called "kasumi". Kasumi can be translated as a fuzzy or wavy appearance and the root word is used to describe the fuzziness things have from a distance over hot summer ground, like a mirage. Sort of the opposite of a mirror. With the jigane polished to a dull darker look you can see the folded character and the imperfections and handmade qualities of the wrought iron. Old antique jigane is made from antique recycled iron and is generically called rintetsu. Recycled boiler plates and ships anchors or bridge wrought iron is referred to as Watetsu and it is usually softer and better for the backs of plane irons but too soft for chisels.
One of the tips in sharpening with hard stones and to regulate the stone abilities and performance is by how much water you use on the stone. In general I only splash some (virgin, distilled or clean rain) water on the stone to begin sharpening. Do not soak the stone, if you do it will melt over time or may delaminate. Just splash some clean dedicated water on the stone and begin with short even strokes. Adjust the downward pressure and adjust the amount of water, the stone will respond in different ways with amount of water and pressure. If you feel the stone is not engaging the steel, splash some water and take your finer diamond plate and with 4 or 5 light strokes create a slurry on the stone surface. In doing so contrive to leave as much of the slurry on the stone and less on the diamond plate. This slurry will help to build more paste or slurry while sharpening and will aid in sharpening.
Do not use a traditional Nagura stone on a Suita stone to build a slurry. Suita stones are call suita because in the grain of suita stones is a very fine pattern of "Su" or beehive pinholes formed by ancient gasses. Suita is 2 characters and translates as su=beehive voids like a beehive and ita=layer or strata. Suita stones always have the pinholes and you can see them with a magnifying glass. The small holes will hold and harbor the larger course grains of nagura stone and they will scratch you blade because they are not as fine as the suita stone that you are using. Most nagura is in the 15,000 grit. So only use Nagura on Tomae stones like Narutaki or Nakayama stones that do not have Su. On Tomae stones the nagura particles will remain on the surface and will be rolled around and pulverized through the sharpening process into smaller particles suitable similar in diameter with tomae type stone it is being used with. Again, with suita stones the nagura particles get trapped inthe su and remain there as full size particles and do not get crushed into finer sizes.
After you are done using your suita stone you do not need to wash it if you can keep it in a cool dust free dry place. The paste that you have build will facilitate you next sharpening so you do not need to build a slurry again from scratch.
Remember that water can transfer containments from stone to stone as will your hands. Keep the clean dedicated water for your natural finishing stone separate from the water you use for your synthetic and courser grade stone. You do not want any 1000 grit particles from another stone degrading you fine awasado matrix. If you ever discover renegade scratches or particles coming from you awase toishi surface, try lightly resurfacing the toishi with a diamond nagura (diamond plate) and wash off the slurry with clean, clear water. The diamond plate and water should flush out the loose foreign material from the su holes so it can be rinsed off.
As you are using your tennen toish always try to incorporate all areas of the stone into the sharpening regime just as you would with any stone, and flatten it with a clean diamond plate when you feel it is needed.