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Frog Restoration Questions


GeorgeH
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This frog is from a bow by a very good German maker, c. 1880. The stick is in excellent condition. My questions are regarding the restoration of the frog:

1) How does damage like this happen?

2) Is it possible to repair to be invisible or almost invisible?

3) The mother of pearl in the slider and remaining eye is almost bleached white-looking and the surface appears deteriorated. I'd like to replace them. Is there a historically-correct color I should use? Was the original a smooth white?

Audience_side1.jpg

front_side1.jpg

players_side1.jpg

slide1.jpg

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10 minutes ago, GeorgeH said:

This frog is from a bow by a very good German maker, c. 1880. The stick is in excellent condition. My questions are regarding the restoration of the frog:

1) How does damage like this happen?

2) Is it possible to repair to be invisible or almost invisible?

3) The mother of pearl in the slider and remaining eye is almost bleached white-looking and the surface appears deteriorated. I'd like to replace them. Is there a historically-correct color I should use? Was the original a smooth white?

1) Impact? The wood is thin at that point and slightly brittle.

2) Yes, almost invisible.

3) I don't know.

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16 minutes ago, fiddlecollector said:

Take the slide out and clean it , i can see pink and green hues showing faintly underneath the white  powdery surface.

Does this material oxidize on the surface over time?

Edit: Another picture:

Slider3.jpg

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Its acid damage either off hands or out of atmosphere . It causes a powdery opaque  surface if the piece hasnt been cleaned for years like it looks in this case. Just rub it with some fine micromesh or something like autosol which is alkaline and shouldnt damage the pearl.

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59 minutes ago, GeorgeH said:

This frog is from a bow by a very good German maker, c. 1880.

Audience_side1.jpg

 

Are you sure that it's a German bow? This frog with the pinned adjuster could also be French?

For the repair you can use both hide glue and super glue. In this case super glue would give a better connection with the metal slide. It's important to clean and smoothen the surfaces and find a matching piece of ebony in regards of colour and grain, so it can be repaired nearly invisible.

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Just now, Blank face said:

And it's sure that the frog belongs to the stick?

Yes. The frog fits perfectly to the stick, and the underslide is screwed with brass screws, not pinned. The adjustor is exactly characteristic of this maker down to even the conical tip of the screw. 

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3 hours ago, GeorgeH said:

...Is it possible to repair to be invisible or almost invisible?...

Yes.  Invisible to casual inspection from a foot or two away.  Not invisible to close inspection with magnification.

It's delicate work and it's not a simple job.  It involves removing the underslide, preparing a good gluing surface where the jagged edge is now, gluing on a piece of replacement wood, reshaping the replacement and re-installing the underslide.  A quicker job on a cheap bow can be done by filling with ebony dust and super glue and trimming the fill.

 

3 hours ago, GeorgeH said:

...The mother of pearl in the slider and remaining eye is almost bleached white-looking and the surface appears deteriorated. I'd like to replace them. Is there a historically-correct color I should use? Was the original a smooth white?

I see this type of deterioration on some old bows, but not on most.  I think it is caused by a chemical reaction to players' perspiration, with some players being quite reactive but most players being minimally reactive.  I have seen extreme cases where the reaction has progressed to the point that the mother-of-pearl has been eroded completely through.

In mild cases, as your slide appears to be, I find simply removing the surface corrosion with fine steel wool to be sufficient.  (This should be done with the slide removed from the frog.)  In the worst cases, the pearl can only be replaced.  Different makers and schools of making used different types of pearl, some of them being plain white and others having various colors and figures.  To replace your missing eye I would look for one that matches the one that's still there.  I can usually find a good match in my collection of old pearl eyes that I have salvaged from destroyed frogs.

The decision of whether to steel wool or to replace the pearl is a judgement call based on how badly it's eroded, the bow's value and the owner's preferences.  Since a little erosion is normal on an old bow, a new slide can look out of place, and when I install a new slide on an old bow I usually etch it with acid to make it look aged.

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8 minutes ago, Brad Dorsey said:

It's delicate work and it's not a simple job.  It involves removing the underslide, preparing a good gluing surface where the jagged edge is now, gluing on a piece of replacement wood, reshaping the replacement and re-installing the underslide.

Though I agree with all other points, it's not necessary to remove the underslide if it's not damaged or deformed. The replacement wood can be adjusted to fit the surfaces, if they are prepared and straightened. This would also save the original srews, which are an identification feature.

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3 hours ago, Blank face said:

...It's important to clean and smoothen the surfaces and find a matching piece of ebony...

 

34 minutes ago, Blank face said:

...it's not necessary to remove the underslide if it's not damaged or deformed. The replacement wood can be adjusted to fit the surfaces, if they are prepared and straightened. This would also save the original srews, which are an identification feature.

 

I don't think it's possible to properly transform the jagged edge into a good gluing surface without removing the underslide.  And without a good gluing surface, an invisible joint would be impossible.

I hadn't noticed that the underslide is screwed, and this makes the underslide a lot harder to remove than if it were pinned.  Sometimes these screws are impossible to unscrew.  If they could not be unscrewed, they would need to be milled out and replaced.  I think that replacing the screws would be preferable to a poor glue joint, because the glue joint is always visible and the screws are only visible when the frog is removed from the stick.

I suppose that on a truly historically important bow the best option might be the cheap ebony dust/super glue fill, because this requires no removal of original wood, no messing with the screws and the fill is removable.  But I assume that this is not the type of bow we are discussing here.

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55 minutes ago, Brad Dorsey said:

I suppose that on a truly historically important bow the best option might be the cheap ebony dust/super glue fill, because this requires no removal of original wood, no messing with the screws and the fill is removable.  But I assume that this is not the type of bow we are discussing here.

It's a good bow worth repairing in a way that preserves as much of the original parts as possible, but I'd prefer to have a new piece of ebony glued in even though I know some wood will need to be removed to prepare a proper gluing surface.

 

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4 hours ago, Brad Dorsey said:

I don't think it's possible to properly transform the jagged edge into a good gluing surface without removing the underslide. 

This I would dispute. I did.Of course it's necessary to support the metal slide with a fitting stick or another fitting piece of wood, but it needs just a sharp tool.

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5 hours ago, Brad Dorsey said:

I suppose that on a truly historically important bow the best option might be the cheap ebony dust/super glue fill, because this requires no removal of original wood, no messing with the screws and the fill is removable.  But I assume that this is not the type of bow we are discussing here.

I like this method. I tried it immediately after Jerry Pasewicz reccomended it. 

I find it's easy to get a close match to the colour.

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This is a common repair on older bows, and one that can have excellent, nearly undetected results that are very difficult to detect unless closely examined under a powerful light or a black light. 

I have a few comments...

  • The fact that the button rings are pinned is no indication whatsoever of country of origin. Pin number and placement might hint of an individual maker, but not country or origin. Pins in buttons are pretty ubiquitous. 
  • Your mention of the silver underslide having been installed with brass screws would place the date of the frog well into the 20th century. Most examples of early German bows with screws have iron screws in them, not brass. I don't know when the earliest examples of brass screws were installed, but to me, that is a mid-20th century characteristic.
  • Removing screws in underslides is often not too difficult if you use heat and the appropriate screwdriver. Most of the time, the only screws that I have to mill out are the rusted-in iron ones, but the vast majority of the underslide screws in frogs that I restore, I can back out and then re-install them after the work on the frog is complete.
  • The pearl slide is cracked. You should just plan on replacing it, and using eyes that match. Speaking of the appropriate pearl...   Look up examples of other bows by that maker as see what was originally used. When restoring historic bows, as much as possible, use what the maker originally used. Also make sure to fit the slide and install the eyes with the flame oriented correctly.

Yes, you need to remove the underslide to do a good replacement on the missing ebony. You will not have good results if you try to fit in a piece that big without removing the underslide. The missing chunk of ebony goes deep enough into the frog that the lowest part is below the center facet of the underslide. In other words, if you just try to graft on a piece, you will have gaps. Furthermore, given the location (at the toe of the frog), every time the bow is tightened, the pressure of the hair tension will pull the frog forward onto the toe of the frog, putting pressure against the glue joint. This will eventually cause the new piece to fall out. Besides all that, removing the underslide will enable you to clean all the old glue and mess out from the channel of the underslide. The pictures above make it look like the underslide is already loose from the glue in the frog. At the same time, the back corner of the underslide can also be straightened while it is off of the frog.

What needs to be done is to remove the underslide first. Resurface the break in the frog, removing all old glue and splinters. This can be done with a flat glue surface (planed, chiseled, or filed) or using a ball-end milling bit in a mill (creating a radiused gluing area). I prefer the use of the ball-end mill because it gives more gluing surface--and I can go a little deeper, angled into the center channel of the frog. The additional depth and gluing surface into the frog gives more wood that is replaced, rendering a stronger repair that will resist splitting out again in the same location. The idea is similar to what a soundpost patch does in an instrument--the patch reinforces a high stress area that would likely suffer failure again without the additional support.

After the surface is prepared, fit in a matching piece of ebony--paying attention to the grain, the angle and the fleck in the new wood. Glue it in with your choice of perfect glue. Then use a chisel to re-establish the underslide channel. Reglue the underslide, re-install the screws, and then reshape the outside contour of the frog.

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41 minutes ago, Josh Henry said:

Your mention of the silver underslide having been installed with brass screws would place the date of the frog well into the 20th century. Most examples of early German bows with screws have iron screws in them, not brass. I don't know when the earliest examples of brass screws were installed, but to me, that is a mid-20th century characteristic.

Hi Josh,

Thank you so much for your detailed and thoughtful answer. I have attached a picture of the button and underslide. The screws are rusty brown, so I was wrong, they are probably iron, not brass. 

I am taking it to an expert in historical bow reconstruction tomorrow. This thread has been very helpful to me in thinking about alternative for the restoration.

Again, many thanks to all who offered suggestions. I will post after photos when the work in complete.

George

06underslide_and_screw.jpg

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Thanks for the additional pictures George. I would be willing to bet that once the gunk is scrubbed away, the heads of those screws will reveal that they are iron, not brass. I do find it interesting that the front screw has a slot that is not centered. This might not mean anything, or it might indicate that these screws were individually made by hand rather than mass produced. 

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2 hours ago, Josh Henry said:

...I prefer the use of the ball-end mill...

Josh,  Can you tell me more about this use of a ball end mill.  What size(s) of mill(s) do you use?  Is one of those vises that pivot on two axes essential?  How do you clamp the frog in the vise without crushing it?  Do you put some kind of reinforcing or packing on the outer surface(s) of the frog to stabilize the edge(s) of the cut?  What spindle speeds do you use?  Are carbide mills the best for this?

I have the IPCI and Regh bow repair books, but I thought you might have some different tricks up your sleeve.  I have a bench-top mill-drill that I haven't used much, but I have used it to mill out rusted underslide screws and seized eyelets and screws.

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Hi Brad. Check out this article posted a few years ago by Kari Azure from the Triangle Strings (Jerry Pasewicz's shop). This article highlights the main techniques.  https://trianglestrings.com/cheval/

I use a Sherline mill, model 5400. Yes, I have an angle milling vise and I do have to get creative in holding the frog. Most often, I use cut wine corks to hold the frog in the vise. I do reinforce the fragile edges with tape to keep things from splintering. As mentioned in the article, I also will use thermal set dental cast when needed, but more recently, I prefer to use Thermo-loc to help hold oddly-shaped pieces (https://www.riogrande.com/product/grs-thermo-loc-fixturing-compound/118131).

Feed and spindle speeds are generally not much of an issue because I'm only milling out wood, not metal. My mill is a manual mill, so feed speed is whatever I crank the handwheel, and spindle speed is usually what the machine sounds good when it is cutting.

As far as the ball end mills, I have them in 5 or 6 sizes, as small as 1/8" up through 5/8." The size I use depends on the job that I need to do. The most common sizes that I use are 3/16" or 1/4" for single-sided chevals or 1/2" if I need to go deeper and get both sides and reestablish the entire underslide channel. For the repair in this thread, I would probably use one of the smaller mills--maybe the 3/16" if I could orient it as needed and remove the necessary wood. The idea is to remove just enough original material on the outside of the frog to give a perfect glue join, and also to replace enough wood next to the underslide (or inside the frog) to give durability and strength to the frog.

I should also mention that I also have a Sherline lathe. A lathe is necessary in doing this technique to turn down the ebony piece into a matching diamater (as the ball end mill) to fit into the radiused void cut into the frog. 

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  • 2 months later...

Follow-up:

I received this bow back from @Josh Henry who did a magnificent restoration on it. It is a fine bow by Johann Christian Suess. All the original parts of the frog were retained, and only the minimum amount of wood was replaced. And, importantly, Josh was a great person to work with.

The "Before cleaning" pictures are at the beginning of the thread. Here are some Before-After restoration pictures:

 

Frog_Before.jpg

frog_after.jpg

frog_after2.jpg

Frog&Head_Small.jpg

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