Freedom of Choice / Screwed by Choice
By Dale Sardeson, MA Conservation Studies specialising in Clocks
When I tell people what I do, some of the most common responses
include something along the lines of "I can't imagine working on
such tiny parts" or "You must have to be so accurate". People seem
to imagine a hunched, wizard-like character with multiple levels of
magnification attached to his face, delicately fettling up a tiny
wheel or spring. Don't get me wrong, that sort of thing is very
often part of the process; but for me, the most difficult part of
being a clock conservator, the things that I go over and over in
the shower, the bit that I rehearse in my head and question before
and after I've done it is what happens before I even take any tools
out of my workbench drawer - the decision-making process.
Deciding which course of treatment to take on an object can be a near-impossible task, and even after I've finished working on a clock and it's ticking away happily on a test stand, I'll still be wondering if there was something I should have done slightly differently. I'm sure anyone who works in any conservation specialism can identify, but for anyone who thinks I sound a bit neurotic, you're probably right, but let me give you an example from a recent project to illustrate what I mean.
Figure 1 shows the snail that governs the striking on an early 19th century swiss clock, attached by two screws to the wheel behind it that controls its position. I won't get caught up on an explanation of its seemingly bizarre shape and how it relates to the function, that is a conversation for another time.
The issue I discovered with this group of components when disassembling them for cleaning is that the shaft of one of the screws (the one on the left in Figure 2) was so burred up and in such poor condition that it had stripped the thread from its hole and was basically doing nothing anymore. Comparing it to the period screw on the right of Figure 2, it is also clear that the faulty screw is a reasonably modern replacement.
One of the key tenets of conservation is that of 'minimal intervention', which is sufficiently vague to be the cause of endless conversation and debate between those practitioners who are prone to intellectual activity of an arguably navel gazey nature, of which I am definitely one.
Minimal intervention can be a tricky matter to negotiate when working on dynamic objects, as we have to consider what the end goal is - do we want something that is stable, or do we want something that is going to function? The minimally interventive course of action in each case will be different. Equally, if we're to work on the principles of 'value' set down by Appelbaum (which I personally tend to as I find them a useful framework), then a course of action that causes minimal impact on one value may have a more significant impact on another.
With all that in mind, I had to decide how I was going to address the issue of the worn-out screw thread. My initial thoughts looked something like this:
Option 1: Broach out and plug the
stripped hole, re-drill and re-tap the thread.
Pros: Means an exact replica of the other screw dimensions are possible. Also, no intervention with the wheel hole.
Cons: Heavily interventive (in comparison with the other options) to the snail. The plug material would be visible thus reducing aesthetic value.
Option 2: Make a new thinner and longer screw to go
through the hole without touching the sides and be secured on the
front of the snail with a nut.
Pros: No intervention of historic material at all.
Cons: Aesthetically unattractive. Adding more material to the clock that was never there.
Option 3: Make a new thinner and longer
screw to go through the hole without touching the sides and be
secured by a decorative ring that goes around the snail arbor, with
the ring having in it another hole wherein the other screw end can
Pros: No intervention of historic material at all. An aesthetically much better solution than option 2.
Cons: Adding more material to the clock that was never there. Even if well documented and stamped, the new decorative ring could easily be interpreted in the future as a replacement for a part that originally existed, when in fact it is an entirely fictional addition to the history of the object.
Option 4: Re-thread the stripped hole with a bigger
thread, having a Minor Diameter that matches the existing size.
Slightly open out the hole in the wheel to allow this marginally
bigger screw through.
Pros: Less interventive to the snail than option 1. Aesthetically the best choice without adding extra material to the clock.
Cons: The only option that requires intervention to the wheel hole.
Firstly, with my "minimal intervention" hat on, options 2 and 3 seemed to be the obvious shortlist, but I've been caught out in the past with adding new components to an object and I am of the opinion that it really interferes with the interpretation. One would hope that the danger of an entirely new component being mistaken for a replacement of something that used to be there would be minimal, given transparent and coherent documentation. However, we can't even guarantee that this documentation won't be lost in a museum environment, let alone in the home of a private client, which is where this object lives.
So, I wrote off options two and three, and looked again at the first and fourth. Re-examining the existing hole in the wheel for the screw, I could see that it had already been previously intervened with in order to fit the replacement screw in. This made me feel much better about the small intervention to the wheel that option four required, as that hole had already lost its historic value due to the earlier modern intervention. Consequently, I settled on option 4 as the one that preserved the most aesthetic value, whilst balancing material intervention to the snail and the wheel.
Reading this you might wonder why I'm fretting so much about tiny losses of material like this, after all, it was only millimetres. But millimetres make centimetres, and all historic material has value; we have to draw a line somewhere, so I aim for zero and treat anything more than that as a serious decision that requires consideration.
Even with the work done, and a result that I am happy with, I still wonder whether or not I should have chosen a different option. I feel like my justification is sound, but I can see why any of the other options could also be justified. But in all decision-making processes there comes a point at which you have to act, this component was not functionally stable with only one effective screw, so something had to be done.
But I still occasionally think about it in the shower.