The ground on the top plate of an instrument - how good or how bad can it be?

[Andreas Preuss]

Regardless if (or if not) the ground is the magic trick to get the ultimate sound (are we talking about secrets??), I prefer to think about it like what can the ground do and what it can’t do in relation to the sound. And for making a discussion  as focused as possible I want to limit it to the top plate assuming that it has there most impact. 

(Note: please no discussion about wood treatment, that’s something different) 
 

While a good ground can enhance the optical impression of the color varnish, this does not necessarily mean that it works best for the acoustics.

I am not interested here in the Cremonese ground or other old recipes. (We assume it is the best ground we can get, but is there any real evidence for it?) I am more interested in a general view. So I am asking myself a few questions. 
 

1. How does the sound change with a hard ground versus a soft ground? There are some pretty intriguing statements. No one less than Roger Hargrave says that since he is using the POP ground he is not afraid any more that his violins have no (good) projection in a hall. (And he is certainly someone who knows what he is talking about) 

Soft ground materials like propolis seem to have lost focus in the violin world. 

2. Does weight matter, or can we ignore it, because it is insignificant? If I try for example the extreme case of using a lead pigment what would this do? (In practical terms it would be possible to cook Massicot (lead orange) in linseed oil to dissolve it entirely.)  It seems that some modern noise absorbing varnishes use heavy ingredients to absorb engine sound from cars. So would a heavy ground rather risk to mute the sound? Or could certain formulas filter part of the spectrum? Then it would be desirable to filter a region that should be rather low, the nasal Formant for example. 

3. if the ground is not only in the wood but raises above (presumably making the halo effect) what happens then?  And in theory if we would just continue and make the ground very thick so that it reaches the weight of the ungrounded plate? (Would be intriguing to think that the thickness would have a certain desirable effect.)

4. Would it make a difference if the plate is sandwiched in between the ground which means the same ground is applied in the inside of the instrument too? 
Or, if the ground is only on one side, does this create an ‘imbalance’ for the vibrating plates? 

5. Last not least the penetration into the wood should in theory make a difference. We could see it as an anchor effect. For example it should make a difference how much glue is thinned down if it is applied as a ground. (And can have pretty attractive looking results too) 

6. And one more: is there any (fundamental?) difference between mineral, resinous, glue based, emulsion or oil ground? And for minerals, dies size of the particles matter? (In theory a Nano particle filler should be somewhere different to much bigger particles, not only for the depth of penetration but also the density of the particle layer.) 

I would suggest that answers refer to the points I made and if someone can think about something which was not on my radar it would continue as number 7) 

Hopefully this thread won’t end   in a silly YouTube as defending argument to something which is not related to this topic) 

Let’s have a debate/discussion which is on-topic and not off-topic.Knowing how heated argument exchanges can become, disagreement is welcome, but with respect to other participants please. (Stay calm, ladies and gentlemen)

 

 

 

[JacksonMaberry]

I do think this is an interesting suite of topics worth discussing. 

Thus far, I have made instruments with either Roger's PoP method or my own formulation of an oil-resin ground based on Echard's findings. I feel that the latter has a more pronounced beneficial effect on selective damping due perhaps to penetration (~ 10 microns), which reduces sibilance on the E and seems to favor robustness on the lower strings. I tend to build all violins on the same model, after the 1668 Stainer in the NMM and have the good fortune of working from the same logs of maple and spruce, but even so I think an apples to apples comparison of ground needs to be made carefully 

[David Beard]

What an interesting topic!

Clearly ground and varnish alter appearance.  But, is it so clear how much or how little either contribute to sound?

Thickness of even a thick finish is well less than 100th the spruce wavelength of even frequencies normally regarded as too high to hear.  So, it isn't reasonable to think of waves travel through the varnish.  

However, varnish and ground are part of the surface boundary between the vibrating wood and the air being vibrated.

Just as surfaces in a room greatly impact vibration reflections, and in a frequency dependant way, we can expect the physical boundary in violins from wood to air to matter.

[Andreas Preuss]

4 hours ago, JacksonMaberry said:

I do think this is an interesting suite of topics worth discussing. 

Yes, and with all the points I tried to separate, it looks pretty complex.

 

4 hours ago, JacksonMaberry said:

my own formulation of an oil-resin ground based on Echard's findings. I feel that the latter has a more pronounced beneficial effect on selective damping due perhaps to penetration (~ 10 microns), which reduces sibilance on the E and seems to favor robustness on the lower strings

Though there is some intuitive guesswork when judging the results, over time we certainly form our convictions about one or the other ground. if you work already from the same tree that’s certainly a huge advantage. 
 

When it comes to oil rosin ground (supposedly very similar to varnish) I think the degree of penetration can make quite some difference. Rene Morel who used a cooked rosin ground (he made the recipe a secret and only told us to cook rosin and watch the smoke) applied it actually with a heat lamp to get a very deep penetration. (I am not sure if he mixed oil into it, probably not) 

Did you ever make a sound graph comparison of BEFORE and AFTER? 

——————-

I think Roger Hargrave made a pretty bold statement and I have no doubt that it works for him. Since he is not the guy who sits in an acoustic lab to provide details about frequency shifts and stuff like that,  my guess is that the POP just resonates itself in some high frequencies. 
My intuitive guess is that it kicks in where the mechanics of body resonances don’t work any more, so above the bridge hill where we perceive rather some ‘white noise’. I am also guessing that some of the texture in the sound comes from such a ground almost as if the POP particles would rattle  with the vibration. (I am sure they don’t ) 

[JacksonMaberry]

4 minutes ago, Andreas Preuss said:

Yes, and with all the points I tried to separate, it looks pretty complex.

 

Though there is some intuitive guesswork when judging the results, over time we certainly form our convictions about one or the other ground. if you work already from the same tree that’s certainly a huge advantage. 
 

When it comes to oil rosin ground (supposedly very similar to varnish) I think the degree of penetration can make quite some difference. Rene Morel who used a cooked rosin ground (he made the recipe a secret and only told us to cook rosin and watch the smoke) applied it actually with a heat lamp to get a very deep penetration. (I am not sure if he mixed oil into it, probably not) 

Did you ever make a sound graph comparison of BEFORE and AFTER? 

——————-

I think Roger Hargrave made a pretty bold statement and I have no doubt that it works for him. Since he is not the guy who sits in an acoustic lab to provide details about frequency shifts and stuff like that,  my guess is that the POP just resonates itself in some high frequencies. 
My intuitive guess is that it kicks in where the mechanics of body resonances don’t work any more, so above the bridge hill where we perceive rather some ‘white noise’. I am also guessing that some of the texture in the sound comes from such a ground almost as if the POP particles would rattle  with the vibration. (I am sure they don’t ) 

I haven't made before and after plots, as I am about as low-tech as Roger. It's all just experiential. Very interesting about Rene's approach. Tom Sparks talked about doing something similar, but with a hair dryer for heat. With the research available to us today, I think oil is every bit as important, if not moreso, a component than the resin. But as we know with linseed oil there is a huge amount of variation in properties from the available sources. There are also so many ways to wash or otherwise prepare oil, and so it becomes extremely difficult to talk about the effects with any authority. 

I do think penetration is important and, when done thoughtfully, beneficial. Michelman's extreme approach of total saturation is not good, but a bit of penetration certainly enhances the optical properties of ground-wood interaction and, in my experience, can do wonders for the tonal results too.

[Andreas Preuss]

11 minutes ago, David Beard said:

What an interesting topic!

Clearly ground and varnish alter appearance.  But, is it so clear how much or how little either contribute to sound?

Thickness of even a thick finish is well less than 100th the spruce wavelength of even frequencies normally regarded as too high to hear.  So, it isn't reasonable to think of waves travel through the varnish.  

However, varnish and ground are part of the surface boundary between the vibrating wood and the air being vibrated.

Just as surfaces in a room greatly impact vibration reflections, and in a frequency dependant way, we can expect the physical boundary in violins from wood to air to matter.

When just talking about the boundary, we often forget that the inside of a violin has almost as much surface as the outside. Which surface matters more? I sometimes wonder what would happen if we apply some sound absorbing stuff in the inside of a really good sounding violin (I don’t think this test can be made on a cheap factory sounding VSO) We would of course assume this has a negative effect, but maybe not. 

[Andreas Preuss]

20 minutes ago, JacksonMaberry said:

Tom Sparks talked about doing something similar, but with a hair dryer for heat

In my experience a heat lamp works better.
 

We might even ponder about a combination of both methods.  

[JacksonMaberry]

17 minutes ago, Andreas Preuss said:

In my experience a heat lamp works better.
 

We might even ponder about a combination of both methods.  

I would think heat lamp would be better, though I have used neither. The air flow of the hair dryer would have a dessicating effect. 

 

Regarding the inside surfaces - I think some kind of coating inside is important, too. I scrape and burnish the inside surfaces just as thoroughly as the outside. Because my ground is essentially a type of oil varnish which requires UV curing, I don't use it on the inside. Instead I size with shellac. I don't like protein coatings anywhere because of the hygroscopicity. I would rather the coatings help safeguard the wood from atmospheric conditions than exacerbate them.

Maybe I should use my ground on the inside some time and see what effect it has on sound and performance.

[Don Noon]

I can't go point-by-point answering all of the questions posed (or even really ANY of them, with confidence), but I can add a few observations and opinions...

-There is a very clear, distinct characteristic tone of an unvarnished violin that I can only describe as raspy or buzzy.  Therefore, any coating must be doing something... most likely some degree of damping, and secondarily (IMO) modifying the longitudinal/crossgrain properties.

- In test samples, oil-bearing coatings add significant damping.  Protein and resin/solvent add less damping, usually.

- In one test violin, I coated the bare spruce with polymerized tung oil.  It sounded muffled... i.e. overdamped.  Perhaps over a period of years it might improve, but I didn't wait that long.

- Since the focus is the spruce top in this thread, "penetration" might need some consideration.  Spruce is pretty impenetrable crossgrain and tangential, so the only real penetration would be via endgrain, or the sloped surfaces near the endblocks.  However, there would be one or two cells worth of open and cut walls everywhere else, and "penetration" there might be more about wetting and filling the open surfaces as compared to bridging them.  Penetration in figured maple is a very different world.

I should do more acoustic tests of ground and varnish, but for now I'm just using oil-free coatings on the bare wood to seal and partially fill the spruce and keep damping low-ish, as the subsequent oil varnish will add damping.  On the interior, I like to use a light casein coat with anti-fungal and anti-bug additives... a fraction of a gram, with probably no significant tonal effect.

In any event, I think that keeping the coating thin and damping low is a good thing, as I have not yet made a new, varnished violin that sounded raspy/buzzin and underdamped.  Most great old violins don't have much varnish left, and just have a very thin polish on the wood.

[Greg Sigworth]

Thank you for this discussion. I have read Roger Hargrave's ground application and would someone please explain what is POP identifying? I don't know the term. Also, in a different direction, In the book "The Violin Maker" Sam Zygmuntowicz is said to start the finishing process by applying an early coat of some light brown liquid with a brush and later using his fingers and done under a heat lamp. Did he work for Rene Morel for a while?  In the book above Zygmuntowicz is quoted as saying that he believed that the application was to penetrate the wood and strengthen or bind the fibers together. Any more information of this process would be helpful. I hope this this doesn't deviate from the topic. Thanks

[duane88]

POP=Plaster of Paris

 

[Greg Sigworth]

1 minute ago, duane88 said:

POP=Plaster of Paris

 

Thanks, that makes sense. 

[JacksonMaberry]

47 minutes ago, Don Noon said:

Since the focus is the spruce top in this thread, "penetration" might need some consideration.  Spruce is pretty impenetrable crossgrain and tangential, so the only real penetration would be via endgrain, or the sloped surfaces near the endblocks.  However, there would be one or two cells worth of open and cut walls everywhere else, and "penetration" there might be more about wetting and filling the open surfaces as compared to bridging them.  Penetration in figured maple is a very different world.

Very good point!!

[Don Noon]

1 hour ago, Greg Sigworth said:

Also, in a different direction, In the book "The Violin Maker" Sam Zygmuntowicz is said to start the finishing process by applying an early coat of some light brown liquid with a brush and later using his fingers and done under a heat lamp. 

I'm not sure, but my impression is that the book is more from the viewpoint of a non-maker, where there is great mystery in everything.  I quizzed Sam some years ago about his ground and varnish, and didn't get a clear, straight answer... perhaps partly because (as I inferred) he doesn't do the same thing every time.  As I recall, he did disclose that he doesn't use oil finish directly on the wood.

That was as of more than 10 years ago... my memory may be faulty, and he may have changed materials and methods by now.

[Andreas Preuss]

3 hours ago, Greg Sigworth said:

Thank you for this discussion. I have read Roger Hargrave's ground application and would someone please explain what is POP identifying? I don't know the term. Also, in a different direction, In the book "The Violin Maker" Sam Zygmuntowicz is said to start the finishing process by applying an early coat of some light brown liquid with a brush and later using his fingers and done under a heat lamp. Did he work for Rene Morel for a while?  In the book above Zygmuntowicz is quoted as saying that he believed that the application was to penetrate the wood and strengthen or bind the fibers together. Any more information of this process would be helpful. I hope this this doesn't deviate from the topic. Thanks

Sorry about not clarifying POP. 

Sam Zygmontovitch worked for Rene Morel and definitely got inspired by his ideas.  As I recall from the same book Sam shows the author a bin with liquified propolis. And he tells that he doesn’t use it any more because it is too gooey. So all we can learn there is that he apparently was looking for something which hardens. And this is presumably done for the sound not for the aesthetics.

what are your thoughts on this?
 

 

[ctanzio]

Roger Hargrave gives a thorough description on preparing a POP ground in his double bass thread on this forum.

The POP has been thoroughly slaked so it is no longer chemically reactive. So do not think of it as casting the violin top into a plaster mold.

When applied as a thin slurry to wood and allowed to dry, it forms a fine crystalline surface that penetrates the pores and any small imperfections in the wood. It can be smoothed over by rubbing with a paper cloth, and it forms a great grain sealer and filler. I have seen guitar makers use it as a filler to create flawless, highly polished surfaces.

The dried appearance is a white haze that may cause a woodworker some alarm. But it has a refractive index in the same range as most varnishes. So once the varnish is applied, the haze disappears and it becomes transparent.

Given the crystalline nature of the chemical, I cannot imagine it adds any significant damping.

It might add a non-trivial amount of extra weight to a thin plate. I have some POP ground from a recent wood working project and might be able to estimate how much weight it adds per unit area.

It is hygroscopic and will easily absorb water. This might be a concern for violin makers unless the varnish can thoroughly penetrate the POP ground and bind it.

 

[Andreas Preuss]

3 hours ago, Don Noon said:

There is a very clear, distinct characteristic tone of an unvarnished violin that I can only describe as raspy or buzzy. 

The thing is that some varnished violins still have the described characteristic of ‘raspy or buzzy’. In the more polite words of Ray Chen this is ‘textured sound’. 
 

4 hours ago, Don Noon said:

- In one test violin, I coated the bare spruce with polymerized tung oil.  It sounded muffled... i.e. overdamped.  Perhaps over a period of years it might improve, but I didn't wait that long.

Tung oil is said to harden like glass. If it is the same time frame linseed oil is completely stabilizing we are looking on 10 years patience.

Regardless, I wouldn’t categorically abandon all oil based recipes because much depends on how much you eventually dilute it in a solvent like turpentine. I think there was a MN participant who would apply one drop of linseed by radically diluting it in turpentine. I doubt that this has any major effect on the sound in either direction, good or bad.

4 hours ago, Don Noon said:

- Since the focus is the spruce top in this thread, "penetration" might need some consideration.  Spruce is pretty impenetrable crossgrain and tangential, so the only real penetration would be via endgrain, or the sloped surfaces near the endblocks.  However, there would be one or two cells worth of open and cut walls everywhere else, and "penetration" there might be more about wetting and filling the open surfaces as compared to bridging them. 

This is pretty microscopic view, but I don’t completely agree here.

 

We all know that except the x lines which appear if a colorant is applied on the top, all other parts absorb an applied medium. In fact the whitish x appears because there is absolutely no penetration in that area. Therefore it is in my view not only on the sloped surfaces near the end block. You are right that close the end block are the most open pores.

i never made the experiment but measured against its own weight I think a spruce top can absorb more perceptual weight  from the ground than the back.

4 hours ago, Don Noon said:

On the interior, I like to use a light casein coat with anti-fungal and anti-bug additives... a fraction of a gram, with probably no significant tonal effect.

As weak as such a coating might seem, in painting manuals there is always a warning against casein glue ground which risks to deform wood panels over time by contracting forces. And what I have seen in a demonstrating photograph in a painting restoration manual, those panels are really thick. 

Don’t ask me how this works in physics, because just by reasonable estimates this shouldn’t happen. But if so, it would be advisable to apply casein on the inside and the outside to balance the surface contracting forces.

 

4 hours ago, Don Noon said:

In any event, I think that keeping the coating thin and damping low is a good thing, as I have not yet made a new, varnished violin that sounded raspy/buzzin and underdamped. 

Here we hit a little bit the point what sound you have in mind when the violin is finished. Just for my personal taste, I like to have a sound which contains the ingredient of raspy as a sort of spicy additive. 
 

If I would translate this into your approach this would mean close to zero damping effect of the ground, correct?

Is it correct to read from your post that you never tried any mineral compositions like POP on your instruments?

[Andreas Preuss]

44 minutes ago, ctanzio said:

The POP has been thoroughly slaked so it is no longer chemically reactive. So do not think of it as casting the violin top into a plaster mold.

Certainly not. Makes me wonder what happens if you add a very low percentage of normal plaster to your slurry. 

 

44 minutes ago, ctanzio said:

Given the crystalline nature of the chemical, I cannot imagine it adds any significant damping.

Here is probably the point. I would be tempted to read from Roger Hargreaves results that it enhances ‘something’ to the degree that you hear the result. 
 

You are much more fit in physics than I am, so is it simply thinkable that a certain formulation can diminish damping? 
 

Maybe just a completely crazy idea I am pulling here up spontaneously. 
Damping as such seems to be much related on the water content in the wood and if we induce some ground substance which binds this water would this diminish the damping?

[JacksonMaberry]

54 minutes ago, Andreas Preuss said:

Damping as such seems to be much related on the water content in the wood and if we induce some ground substance which binds this water would this diminish the damping?

I would expect the binding of water to rather increase damping. On account of it being damp, and all. =D

[scordatura]

Has anyone played a Roger Hargrave instrument that has been treated with plaster of Paris? If so what does it play or sound like?

[Don Noon]

There's an article on the effects of ground on the frequency and damping of spruce; it's for guitars, so limited to things like shellac and laquer, but might be of interest:  https://savartjournal.org/articles/25/article.pdf

It mostly goes along with my testing results... everything adds damping; some less than others, and frequency change isn't a lot.

[violins88]

That work seems to be pretty well done. H.P. Stephens was 95 when he wrote that up!

[Andreas Preuss]

10 hours ago, Don Noon said:

There's an article on the effects of ground on the frequency and damping of spruce; it's for guitars, so limited to things like shellac and laquer, but might be of interest:  https://savartjournal.org/articles/25/article.pdf

It mostly goes along with my testing results... everything adds damping; some less than others, and frequency change isn't a lot.

Did you test the plaster of Paris ground as well?
 

For different varnish formulas (resinous solutions) I would expect similar results. If the comparisons are made short time after the application it tells probably more about how fast the chosen resinous ground can harden. I am tempted to believe that the differences will even out over a very long time.

I see the difference between plaster and rosin in their hardness and weight. Rosin is only slightly heavier than water (1.07-1.08g/cm3) while plaster is more than double. So just by its weight plaster should dampen more than a resinous ground.(?) However, because Roger Hargraves results indicate the opposite it would mean that hardness factors in more than weight. (?) 

What I absolutely don’t know is if damping is for all frequencies the same. If the ground would dampen only frequencies in a certain range, for example the nasal formant, then it would definitely act in a positive way and this would make some ground formulas better than others. 

 

[John Harte]

On 12/11/2021 at 12:47 PM, Don Noon said:

- Since the focus is the spruce top in this thread, "penetration" might need some consideration.  Spruce is pretty impenetrable crossgrain and tangential, so the only real penetration would be via endgrain, or the sloped surfaces near the endblocks.  However, there would be one or two cells worth of open and cut walls everywhere else, and "penetration" there might be more about wetting and filling the open surfaces as compared to bridging them.  Penetration in figured maple is a very different world.

Don, as you mention, penetration in figured maple is a very different world.  However it does seem that there can be at least some penetration into spruce and maybe more than we might think.  I suspect that some of what I illustrate below may be due to open bordered pits in the cell walls allowing material to cross between adjacent cells.  Note the rows of bordered pits in the longitudinal cells (tracheids) and medullary rays the first photo.  This is the quartered face of European spruce that I bought around 10 years ago.

Around 30 years ago I was able to view a range of ground and varnish systems under SEM, largely on maple.  Having said this, the second photo shows a hide glue size filling a spruce cell, the top edge of which being positioned something like 20 microns below the outer surface.  I have another bad photo showing an end grain slice where glue appears to have made it into the third cell layer below the surface.  However I have no idea what the alignment of those cells might have been relative to the outer quartered surface.

The third photo shows a feature that I have seen in photos of a Strad belly taken under microscope.  This is another of my samples, this time featuring an oil varnish ground showing what I think is varnish having penetrated cells.  Depending on the viscosity of the varnish, this feature can be made more or less obvious.

The final photo is the outcome of a quick and dirty test that I carried out this morning.  The spruce involved is from the same source as that in the first photo.  Using a following scriber I checked the fiber alignment, making sure that this was as parallel to the outer quartered surface as possible.  I then applied some black spirit leather dye to the quartered face, well in from any edge.  The stain was left to dry for a couple of hours.  The piece of spruce was then split through the middle of the area of staining, exposing the slab faces.  These faces were then planed to better reveal the depth of stain penetration.  The thickness of the sample at the point shown is 1.53mm.  If you zoom in you should be able to see a little more detail.  (If anyone wants the full size file please PM me.)

Finally I should perhaps mention a comment made to me some years ago by two people working in a well known restoration shop.  Both independently mentioned having seen spots of material in the base of a soundpost patch bed in a Strad fluorescing the same floury yellow colour as the ground material on the outside surface of the instrument.  From what I gather a through patch was not involved with there being something like 0.3mm of material left between the base of the patch bed and the outer surface.  If this is correct or close to correct in every respect, at least partial penetration of up to 300 microns would appear to be involved..

[John Harte]

@ Andreas

Andreas, there have been a number of papers/articles that have appeared in recent years that consider some of your initial questions.  A starting point might be Martin Schleske's “On The Acoustical Properties Of Violin Varnish”.  I presume you have a copy of this?