Inside Mold or Outside Mold?

[Brad Dorsey]

I thought that corner blocks extending farther into the upper and lower bouts, like this:

…always indicated an inside mold.  And I thought that centered rib corner joints, like this:

…always indicated an outside mold or built-on-back construction.

These two pictures are of the same violin.  How was it built?  What am I missing?

[Davide Sora]

I think it was done on an outside form, trying to mimic the blocks of an inside one. 

Clues that make me think so:
1. The block doesn't fill the entire corner; you can see some glue infill at the tip of the corner. This never happens with the inside form, and very difficult to avoid with the outside form.
2. The pencil marks that delimit the blocks. They wouldn't be useful at all with an inside form, but they would be essential with the outside form if you wanted to mimic the symmetry of the block pairs (left and right) of an inside one.
3. The shape of the parts where the linings meet the blocks, although it cannot be said for sure from the photo. You'd need to see the shape of these points in the section below the linings for further clues.
4. And of course, what you already mentioned: the joint of the ribs in the middle of the tip, which doesn't blend with the longest curve of the block.

[Richf]

Sharp eye, Davide!  I would not have noticed those pencil marks, nor even looked for them.

[Brad Dorsey]

I confess to making those pencil marks.

[Blank face]

Pencil marks at the rib’s upper edges would hardly be present anymore after closing and reopening the box 

Otherwise they definitely are helpful only at Bob or outside mould where the block shape isn’t defined by the construction.

While features like form of corner blocks became more and more insignificant in the 20th century due to attempts to imitate other methods (even symmetrical blocks at inside mould were made with complicated mould shapes) there were also varying forms of outside moulds and combined construction methods established, so things can be very ambiguous.

Below, from an old Markneukirchen workshop photograph, a sort of outside mould which would have allowed to pinch the rib ends together in small holes. The result could possibly look like the joints at the OP.

[Brad Dorsey]

2 hours ago, Davide Sora said:

…The block doesn't fill the entire corner; you can see some glue infill at the tip of the corner. This never happens with the inside form, and very difficult to avoid with the outside form…

This seems like a good clue to me, and having attempted to fit a few corner block into instruments that were made without them, I realize how difficult it is to get a good fit all the way in.

But these blocks seem to fit well all the way in, and when I probe with a sharp point I don’t find any empty space.  Here’s another block in the same violin:

 

[Brad Dorsey]

3 hours ago, Davide Sora said:

…The shape of the parts where the linings meet the blocks, although it cannot be said for sure from the photo. You'd need to see the shape of these points in the section below the linings for further clues…

Can you see any further clues here?

 

[Blank face]

5 minutes ago, Brad Dorsey said:

This seems like a good clue to me, and having attempted to fit a few corner block into instruments that were made without them, I realize how difficult it is to get a good fit all the way in.

But these blocks seem to fit well all the way in, and when I probe with a sharp point I don’t find any empty space.  Here’s another block in the same violin:

 

It’s quite possible that only the very upper point of the block has that perfect fit, but everything below (where you can’t see it without removing the bottom) is hollowed. Similar applies to the mortised linings.

[Andreas Preuss]

24 minutes ago, Brad Dorsey said:

This seems like a good clue to me, and having attempted to fit a few corner block into instruments that were made without them, I realize how difficult it is to get a good fit all the way in.

But these blocks seem to fit well all the way in, and when I probe with a sharp point I don’t find any empty space.  Here’s another block in the same violin:

 

 

Drawing copied from the photo.

 

thats why I’d think it was made on an inside mould.

 

 

 

[Blank face]

1 hour ago, Andreas Preuss said:

 

Drawing copied from the photo.

 

thats why I’d think it was made on an inside mould.

 

 

 

The angle at the right rib seems to be an optical illusion caused by a small bright splinter near the tip of the rib. Without it both lines are straight and parallel like they are clearly at the other corner from the bigger picture.

[Don Noon]

There are good arguments for both, but in a blowup of the first photo I see the corners like Andreas drew, and mostly I think it would be too much of a pain to shape the cornerblocks to fit the ribs that well on an outside mold.  Could be either, but I'd vote for inside mold and a maker that for some reason likes the more symmetrical meeting of the ribs.

[Brad Dorsey]

On 7/2/2026 at 1:18 PM, Davide Sora said:

I think it was done on an outside form…

 

On 7/2/2026 at 4:42 PM, Andreas Preuss said:

…thats why I’d think it was made on an inside mould.

?

[Blank face]

Very unlikely that the rib line doesn’t follow the block at an inside mould construction, with an angle that flat. Mind the gap filed with glue at the other corner. And having a mould like I showed above it’s easy to make a perfect template for the blocks.

[Brad Dorsey]

1 hour ago, Blank face said:

It’s quite possible that only the very upper point of the block has that perfect fit, but everything below (where you can’t see it without removing the bottom) is hollowed…

Good point.

 

9 minutes ago, Blank face said:

The angle at the right rib seems to be an optical illusion caused by a small bright splinter near the tip of the rib. Without it both lines are straight and parallel like they are clearly at the other corner from the bigger picture.

Does this argue for an inside or an outside mold?  Why?

[Blank face]

1 minute ago, Brad Dorsey said:

 

Does this argue for an inside or an outside mold?  Why?

Outside mould, or a sophisticated form of Bob. 
I could say because I’ve seen too many of all types open before to confuse them, that it would be even more difficult to shape an inside mould block that pointy that you don’t get a mitre, while it’s easily approachable when the ribs are clamped/pinched together.

In the end it’s impossible to tell for 100% as long as one didn’t look the maker over the shoulder, but can only go for the most probably. And needs to know the complete instrument to be able to judge if it’s from a school which used inside moulds. 

[Andreas Preuss]

20 minutes ago, Blank face said:

Very unlikely that the rib line doesn’t follow the block at an inside mould construction, with an angle that flat. Mind the gap filed with glue at the other corner.

Depends. We tend to think that the inside mould construction is done in two steps. Glue the c ribs and only after they are dry carve in a second step the other sides of the corner blocks to glue the upper and lower ribs. 

I have made once in an attempt to copy an instrument the ribs on a mould but glue them in one shot. You will make a cut surface at the end of the c ribs to facilitate the joint coming together but it is all together not a very precise method where on one corner it can come out nicely at others you have to live with slight inaccuarcies. And it can also happen that when you cut a spruce corner block the tip pops off. 

[Davide Sora]

4 hours ago, Brad Dorsey said:

I confess to making those pencil marks.

I suspected as much, for the reason Blank Face mentioned, but just in case... 

Well, ignore the clue number 2.

[Davide Sora]

2 hours ago, Brad Dorsey said:

Can you see any further clues here?

 

They've rounded off the edges, so it's hard to tell whether they're perpendicular to the ribs or not. But perhaps not making these details legible could be considered a clue in itself.

[Andreas Preuss]

33 minutes ago, Brad Dorsey said:

 

?

there are also other points you can check. Is there a joint at the lower rib at the lower block? And if, how clean is the joint? Usually it is easier on outside moulds to make ribs in two pieces and some makers used a large(r) ebony strip to 'erase' a sloppy joint. 

How precisely are the top and lower block centered on the center line? If they are off it would rather hint at use  of an outside mould where it can happen that blocks are getting off center when working rapidly.

[Davide Sora]

1 hour ago, Brad Dorsey said:

 

?

The problem is that you can work very accurately and without showing obvious signs of that type of construction even with an outside mold. On the other hand, you can work sloppily with an inside mold, leaving marks that could suggest you used an outside form. For example, the joint at the center of the corner tip can be achieved even with an inside form, if you make corners that are too long and decide to shorten them anyway, cutting into the C rib.

So, without obvious signs, it's hard to say for sure. 

I do not eliminate those obvious clues that "certify" the use of the inside form in my violins, so that no one can raise doubts.

[HoGo]

I use outside form for my mandolins similar to what BF posted above (BTW, the holes at the end of the points are there to allow for glue squeeze out, I made my new from that way after some "experience").  I always put one rib in a bit longer and slightly chamfer the other one so they meet with a tight flat butt joint, then I fit the block so it goes all the way in without opening the tip. No problem at all to get almost zero glue at the meeting point and also a joint that appears like built on outside form with bout rib butted to C rib.

The OP violin doesn't show that butt joint at all even in the one example where one rib overlaps in straight line. IMO, the other rib was just slightly chamfgered to meet at the tip in the form.

[Brad Dorsey]

7 hours ago, HoGo said:

...IMO, the other rib was just slightly [chamfered] to meet at the tip in the form.

Inside form or outside form?

Edit: Since you said, "the tip in the form," you must be assuming an outside form.

[HoGo]

Yes, that's the only type of form I've used.

[Richf]

Here's a photo of a Vuillaume corner, showing his efforts to copy the look of interior-mould construction, but with a small gap at the tip of the corner block revealing its actual exterior-mould origins.  From the Musee de la Musique book "Violins, Vuillaume," page 234.