Recovering Upright Dampers

These dampers are from a Schiedmayer & Soehne overstrung of about 1907 in unrestored original condition. The hornbeam bodies are dirty and stained by old mould. Most uprights have the flat damper felts quilted (German gesteppt), sometimes by stitching but most commonly by pressing and gluing. The treble dampers on this piano are plain flat felt, rather thicker than usual and none too well felted. They are also rather untidily cut. This pattern will not be imitated and the usual quilted felt, made in our own press, will be used. The damper heads are wider than normal.

The reasons for quilting are two. As the picture shows, a block of plain flat felt can easily be displaced so that it does not line up with the strings and damp the vibrations as it should. The quilting not only prevents this, by gripping the felt firmly in the middle, but also allows the player more control over half-pedal effects and the possibility of more gradual damping.

After marking the dampers and making a note of the original scheme, before any cleaning is done the old felt is removed, as shown in the pictures below. First the white felt is quickly torn off, leaving only the layer that is firmly glued to the under-cloth or, on most pianos, under-felt. The head is then dipped carefully in a pan filled to the brim with hot water to which a few drops of washing-up liquid is added. Time enough is allowed for enough water to be taken up to wet the felt and cloth thoroughly.

Once soaked, the dampers are left for as long as it takes for the water to soften the glues completely and allow the removal of the cloth and felt without any effort. This might be 40 minutes if glue of normal strength was used. Some makers used a stronger and more resistant glue and this will require a longer soaking time, with perhaps a second hot dip after an hour or two. In any case it is a waste of time to remove the cloth and felt by any other means before the glue is perfectly soft.

The felt and under-cloth are lifted off effortlessly, leaving only a very thin layer of clean glue and perhaps a little staining. If any effort is required, either more time is allowed or a second wetting is performed. The remaining skin of glue can be easily removed, either while it is still soft or when it is thoroughly dry, using a firm sharp knife held at a right angle to the damper head.

The next task is the thorough cleaning of the damper bodies and heads, which will almost always require a wet cleaning, though occasionally a plastic eraser will give adequate results. In the case of this set a saturated solution of oxalic acid is used. With several applications it would probably be possible to remove entirely the dark brown mould marks (which are like the “foxing” on old books) but a single application will produce satisfactory results in this case. The acid solution is held in a shallow container and a length of pure cotton cloth is soaked in acid, wrung out and drawn backwards and forwards over and round the wooden parts clamped in a vice. Remaining surfaces are cleaned with the damper held in the hand. The cloth should be regularly rinsed in clear water, wrung out and wetted with fresh acid.

The hands should be thoroughly rinsed after work with oxalic acid and the nails scrubbed and rinsed.

Strips of facing cloth are now torn, about ¼” wider than the heads, glued to a head and snipped off. The under-cloth is then trimmed to fit using a thin sharp knife and/or a No. 25 scalpel blade.

Strips of flat felt are now cut for making the treble dampers. The sheet of felt is held steady with weights. The felt is cut at an angle of about 10 degrees. It is then flipped over and cut to width, again at an angle. The straight edge is positioned at each end by means of a piece of card cut to the desired width. The felt is the same width throughout on this Schiedmayer but almost always the width decreases from tenor to treble. The knife should be sharp enough to send the hairs of the arm flying and the felt must be cut through in one pass.

A line of dots is made with a black pencil along the centre line of the wide side of the felt strip. These will be lined up with the blade of the press so that the quilting will run exactly down the middle of the strip.

A line of white PVA glue is now squeezed out along the centre line of the narrow side of the felt and this is worked into the felt by drawing a thick steel needle (made from, say, a length of No. 21 music wire) along the line several times, using great pressure so that as the felt springs up again it sucks in the glue.

The strip is then positioned in the press and clamped down very firmly. The pressure is then released for a moment to allow the glue to be sucked in a little more, and the felt is then left clamped in the press for an hour or two, depending on the temperature and humidity.

The glue should not be allowed to dry out completely in the press but the strip should be removed while the glue is still rubbery and flexible. At this stage the backing felt or cloth would usually be glued on, but in the case of the Schiedmayer the under-cloth covers all the wood of the head and is glued on to the wood in the separate operation already described.

Before the individual blocks are cut in the guillotine, a line is drawn down one edge of the glued side of the strip as a guide. The marked side will always be glued towards the middle or towards the end of the damper head, so that the line of the felt will be just as it was in the uncut strip.

Glue of about the consistency of honey is then applied to the under-cloth and the shaped felts carefully positioned and pressed into contact.

Where there are three felts per damper, the top row is glued first, then the bottom row, so that the middle felt can be accurately centred.