Italian jacks

Instrument Building
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Are Italian harpsichord jacks always fitted with a bit of lead weighting?

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| WPADAMS1
June 30 |

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Are Italian harpsichord jacks always fitted with a bit of lead weighting?

No, not all Italian jacks have such weights.

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Often but not always!
Dongsok

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Why is lead weighting necessary?

David

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| Pickett David Pickett Regular
June 30 |

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Why is lead weighting necessary?

We might debate whether it’s absolutely necessary but, by inference, in the case of short, light jacks, it serves:

  • to enhance the return of the jack, including the passage of the plectrum past the string;
  • to enhance damping.
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Some thoughts on the matter based on observation. Galileo demonstrated that objects of different mass when released will hit the ground at the same time. The only factor affecting any difference is air resistance. So a feather will take longer than a cannon ball. We probably all know this from school (but the full explanation had to wait for Newton and Einstein and even General Relativity and inertial reference frames).

Since jacks have negligible air resistance they will fall at the same rate regardless of having a lead weight.

Now, some jacks in Italian instruments are made from very light fruitwoods and hardly weigh much. This is also the case on many French doubles, where the upper manual jacks can be very short, as well. But a heavier jack has more inertia and therefore able to exert more force, consequently, exactly as @alvisezuani has correctly stated, the return is enhanced by being better able to pass the sprung plectrum over the string. Being heavier the jack can apply more downward force to the dampers. But also, being heavier it can help the key return to rest better instead of ‘floating’ down. Furthermore, jacks encounter friction, even if small from touching the sides of the register mortise, wood or leather. A heavier jack is better able to counter this friction. Because of all the foregoing, the weighted jacks tend to enhance repetition as well.

Apart from that, an action where the jacks are too light does not feel certain under the fingers, and some extra weight helps the playability and feel.

One long term effect of lead in jacks is that it tends to bloom and swell as it oxidizes and you get a white powdery substance that is no good, and you have to pare them down with a very sharp chisel. To slow this we usually put a brush of shellac across them. If you are retrofitting, don’t make the hole too large or you can split the jack very easily, especially if the lead diameter is a tad too big or you hammer it too hard.

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What a comprehensive explanation!
On a side note I wish to state the better working, in my experience, of the side dampers versus flag dampers.
Side dampers don’t need the help from jack weigth to damp effectively. They prevent jacks bouncing on thick strings largely oscillating. They provide “cathedral effect” when the register is off. Finally, they allow a progressive damping, i.e. the more releasing the key, the more damping the string, as opposed to a more “on-off” damping effect of flag dampers.

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Well put Andrew: FRICTION is the matter.
A very short and very low weight jack will not be enough to counter friction against the registers (unless there is no such a friction at all, which is not good either).

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And: side dampers gently push the jack laterally against the jack slot, effectively making the quill-string distance regular. This effect is of course most desirable ehen the slot width is irregular, which sometimes happens in Italians.

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Notwithstanding the erudite explanations above, I would be interested to know what percentage of historical italian instruments were made with leaded jacks. Was the ligher fruitwood used, or oak, or what?

I have weighed ten of the front unleaded fruitwood jacks from my ZHI Italian (including dampers and quills), and the answer is 28 gms, making 2.8 gms per jack – pretty light. There is a reasonable (by no means excessive) clearance between the box guides and the jacks, and the jacks return smartly giving no problems with repetition.

If someone has an italian with lead weights, it would be interesting to know data for them.

David

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Dear All

Thanks to Andrew for mentioning the touch aspect of adding jack weight, rather than just considering the return. For the short, light Italian jacks, weight certainly helps the feel of the action. Here’s a pic of my Grimaldi jacks, showing my graduated leads from bass to treble, where no added weight is necessary.

jacks
jacks1920×583 209 KB

(Sorry, David—I’m unable to weigh these jacks for you until I return to my workshop in a month.)

Regards

Carey

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Thanks, Cary: a super photo! What is the wood?

David

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Dear David

My 1990 Grimaldi has beech Adam Swainson jacks with holly tongues, boar bristle springs and Canada goose quill plectra.

Regards

Carey

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I have two italians (one antique and one zuckermann kit I mad) and I had another and made other two from scratch. None of them had weights. Italian jacks are usually shorter but thicker, sometimes significantly thicker, than French ones, so the weigth should not change a lot. Zuckermann Italian jacks seem as thin as french. My antique has fairly thick jacks, the others I had were as thick (4.5 mm about).
The thickness of italian jacks allows for a good working of the brass spring which needs a thicker jack to not protrude from it.

Keene and Brackley spinet has lead-weighted jacks. Ruckers muselaars, which I’d expect needing to be weighted, are not.

Jack design is an elusive art. :grinning: