II: When marking the inside of a piano
→ See video No.56 "How to mark the inside of a piano"
1. When marking the top of the damper
You can use small round adhesive labels (coloured labels from A-one, Kokuyo, Nichiban, etc., with product names such as "Tack Title"). There is also a "stick and peel" type that leaves no adhesive residue after removal. In any case, it is a good idea to leave the edge of the label floating, rather than sticking the whole label tightly to the damper, so that it can be easily removed after playing.
You can also use Post-it in thin strips, or Blu-Tack (see 3. below). The dampers are delicate and should not be pressed too hard or moved too far backwards or forwards, as this can damage the felt and other parts of the damper. When peeling off the label, it should be done vertically. Do not peel it off horizontally.
Do not use chalk to mark the surface of the damper.
2. When marking the edges of the agraffes, bridges and strings
Post-it or similar, or Yamato's "Sticky Note Memo Roll with Tape Cutter". You can also use Blu-Tack.
(These product names are from Japan.)
3. Marking on the strings
To mark the nodes (of vibration) on the string, you can use a small adhesive labels or Blu-Tack. I (Inoue) use Scotch's "Drafting Tape" which is thin, not too sticky and easy to remove. Blu-Tack, by Bostik (Australia), is an adhesive rubber used for sticking posters on the wall when double-sided tape or drawing pins cannot be used for posters. It's like a kneaded eraser, and can be shaped to any size and length, so that it sticks to the object but does not damage it, and leaves no scratches or sticky residue after removal. However, because of their mass, they must be thin when applied to strings or they will sound as if the strings are muted. There is a similar product made in Japan called "Hittsukimushi" by Kokuyo.
There is also the method of wrapping the string around the knot of the string, but this is time-consuming and tedious, both in attaching and removing the string.
Chalk should not be used.
In any case, if these are used for the lower register windings, it is a good idea to check thoroughly after playing to make sure that there is no adhesive residue inside the windings.
I have seen some tuners mark the strings with chalk or magic ink when tuning, and when I asked them if it was OK to do so, they said it was fine, as they would wipe it off with alcohol later. In fact, what a tuner thinks, says and does varies from person to person.)
4. When marking the surface of the felt near the bridge at the end of the string.
Place a small piece of paper over the area to be marked. No chalk, Blu-Tack or sticky material (including Post-it) may be used. Anything that makes the felt fluffy should be avoided.