Following some recent discussions here, and in particular a suggestion made by Alex, I think that there may be enough interest in approaches to restoration and repair to justify a thread.
Rather than the good the bad and the ugly (sorry I couldn't resist it) the question is hopefully more like - what techniques do we consider good, what bad and what might be acceptable in the case of neccesity?
I think to start with we need to try to define restoration and repair:
Generally within the trade restoration is regarded as being the high ground - there should not be such a thing as a badly restored instrument, though there are plenty of badly repaired ones around. Restoration involves the finest of techniques and the highest of ethics. Everything possible is done to preserve the originality of the instrument, all work involved in every detail is reversible, no compromises are made in the effort made to achieve a perfect result.
Repair is a much broader term. There are indeed ethics of repair, though these do not appear to be held universally - these basically once again state that everything possible should be done to maintain the originality of an instrument, and that all work should be reversible. Repair however exists in the real world - where it is not always economical to go to extreme lengths, using long elaborate techniques on for instance a low end American Conservatory, or a Lignatone Mandolin.
Because of its much broader defintion there can obviously be such things as bad (or indeed ugly) repairs. An obvious example of this would be a crack which has had epoxy resin rubbed into it, or a cracked peghead which has been glued with PVA and had a metal plate screwed over it.
Things aren't always as clear cut as these initial examples though.
Because of the concerns of reversibilty and maintaining originality some techniques which may have been widely accepted in the past (restoration has been developing for about the last 150 years) may no longer be widely accepted. For instance some Violin repairers about 200 years ago used to drill small holes either side of cracks, and stitch studs to the instrument through the holes in order to avoid removing the front. Others would saw down the length of a crack with a fret saw and then put a new piece of wood into the slot that they had created. Strad certainly thought nothing of making a new front for his own instruments if it was cracked - of course he was Strad, and these were his own instruments you may well say!
Of course if anyone else was to make a new front for a Strad much of the world be aghast! Which brings me to the subject of originality. Beyond the example already given the other most common way in which the originality of an instrument is compromised is through stripping and re-varnishing. Quite commonly the process of removing the original varnish also causes other damage to the instrument, particularly as it is often removed by sanding. Often this is done because the person is not aware that it is possible to repair damage to the finish through the process of retouching, or because they don't appreciate the look of an aged and worn finish. In the latter case they should really have bought (or commissioned?) a new instrument.
Other techniques have been abandoned because the passage of time has shown them to create as well as repair damage. For instance it was once common to cleat cracks with vellum. This is obviously easier and so cheaper than using studs made of spruce or maple - as the vellum won't need to be fitted, trimmed or shaped in anything other the most basic of ways. However the vellum moves (tensions and loosens) a lot with changes in humidity, and it is quite common to find two later cracks running up neatly either side of a crack cleated with vellum.
The final classification is the acceptable - when should it be acceptable to ignore the concerns of originality and/or reversibility? This a classification that should only ever affect the very cheapest of instruments which would not be economic to repair properly.
However, as most of us are aware, bowlbacks are undervalued instruments and it's possible that a bowlback might fall within this monetary bracket when the quality of it's construction should place it well above the risk of this treatment.
Personally I think in this case the true value of the instrument should be borne in mind. There are signs that this differential in the values of instruments is starting to dissapear, but in comparison with other stringed instruments bowlbacks are still undervalued. This may mean that until the true values of these are reflected monetarily the best that many fine old instruments can hope for is to be kept in a stable condition in a stable enviroment. This is certainly a more desirable short term solution than subjecting them to devaluing irreversible repairs, in order to more quickly bring them into playing condition. There is not such a shortage of instruments that this should be necessary.
This is a very large subject area, that I cannot possibly cover in a single post such as this, but it's a basis for a discussion at least.
What do you think of the standards of reversibility and originality? Have you encountered situations that would challenge this approach?
I look forward to your comments and observations!