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Usually wood grain of violin back plate is not obvious. But there is some exception such as the ones below. Is it caused by too heavy varnish?

Is the fact that the wood grain is not straight acoustically problematic?

In addition, one of the wood grains is a dark line. As seen from the right picture, that dark line is not just a normal wood grain. Is there any reason for selecting such a wood as back plate?

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  • The thing that seems really striking here is that the grain is running from top to bottom of the instrument; usually that's true on the front plate (which is usually spruce), but the back plate (usually maple) usually has the grain running side-to-side. Nov 30, 2022 at 17:09
  • @AndyBonner I think the flamed pattern is not formed by grain. The grain in usual violins back plate is not obvious.
    – Aqqqq
    Nov 30, 2022 at 17:11
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    @AndyBonner That is not true. Both the top and the back have the grain running vertically, not horizontally. If the grain was aligned horizontally this would make sourcing wood much more expensive, since you’d need a very wide piece of wood. You are most likely confusing the flaming of the wood, which is in fact (more or less, can be a bit diagonal at times) close to orthogonal to the grain. This pattern is formed by the wood not growing straigth, but in ripples.
    – Lazy
    Nov 30, 2022 at 17:35

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The top plate should have grain as straight as possible, since to top is the acoustically most important side of the instrument (it is some sort of membrane, moving the air). The back does matter much less. This is the reason why the top is made of a very straight growing, light and soft wood (spruce), while the back is made from a dense, hard and robust material (sycamore (or outside of europe often maple)).

So probably this will be fine acoustically.

The heavy accent on the grain (and also the coloring of the flame) is caused by directly varnishing the wood with a dark varnish or a varnish with pigments. You need to keep in mind that the grain will lead to parts that will absorb liquids differently well. If you then use any form of stain the parts that absorb the varnish better will accumulate lots of color, leading to darker spots. The dark line is merely a part of the grain that drank a lot of varnish.

This is usually considered unwanted, especially as it ruins the amazing shine you get with figured wood (which is caused be the rippling of the grain reflecting lights at different angles). Of course on the other hand you might be able to get an amazing accent of the grain this way, but usually this is not what we want to go for.

So what is done instead is that the instrument is first coated with either very light varnish or hide glue, sealing the wood. This will then mean that further coats of colored varnish will not penetrate the wood and will form a layer of even color. Also due to the wood not actually being stained the wood remains reflective, giving you the typical shine.

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  • Regarding the dark line: but as we can see from the right picture, that dark line also reflects the light differently from the rest, indicating that the wood kind of "recessed" at that line. I don't think it is caused by "that part of the grain drinking a lot of varnish"
    – Aqqqq
    Nov 30, 2022 at 19:47
  • @Aqqqq The darkness is quite likely due to that part absorbing more varnish (which can also cause unevenness, as the wood the takes in more varnish will swell up a bit, which is why some makers sand down after clear coating and clear coat until the wood does not swell anymore). Now, the reason why this part is taking in much varnish is hard to tell from these pictures along. If might be a weakpoint of the grain. Might also be that there was a crack in that place that was filled up. Or something like that. But it is hard to tell more without directly looking at the instrument.
    – Lazy
    Dec 1, 2022 at 6:59
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based on the backplate image you provided, the black line is not caused by excessive varnish. This black line should be the grain line or vascular bundle of the wood, which is primarily responsible for transporting nutrients from the tree's core to the surface of the wood during its growth process. The grain lines are formed due to specific circumstances during the tree's growth, which may include environmental pressure, natural disasters, pests and diseases, damage, or other external influences. When trees are subjected to these influences during their growth, they can cause abnormal distribution or stagnation of vascular bundles, resulting in the formation of a line. Its impact on sound quality is not significant. However, it does affect the aesthetic appearance of your violin's backplate and can also have an impact on the structural integrity of the wood, making it more prone to cracking over time. Unless there are special reasons, I would recommend choosing one of the following types of backplates. enter image description here

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