This is a manufacturing experiment of Linoxyn, one of the varnish materials for violin. Learn how to shorten the drying time by forcibly supplying oxygen during natural drying of linseed oil, as well as the experimental process and results.
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Linoxyn, one of the varnish materials for violins, is a resinous substance produced by oxidation of linseed oil. It is known to have excellent properties as a painting material for violins, but there are not many people who use it because it is very difficult to manufacture. In this study, we will consider factors that can shorten the time of natural drying of linseed oil and try to confirm it through experiments. The chemical theory is omitted and the changes and results of linseed oil are mainly described in terms of the phenomena observed during the one-year experiment.
1. How to Make Linoxyn
When linseed oil reacts with oxygen, it is converted into a soft, elastic semi-solid resinous substance. This changed substance is called Linoxyn. Therefore, in order to obtain linoxyn, linseed oil must be oxidized. Natural drying (oxidation) method is to allow it to be oxidized naturally. Chemical method refers to forced oxidation using a certain substance.
1.1. Natural Drying Method
This method involves placing linseed oil in an open container and allowing it to naturally oxidize. It has the advantage of obtaining linoxyn of stable quality, but the time required is too long. The exact time required is not known, but there is an opinion that it takes at least 5∼6 years or more. During such natural drying, it is necessary to prevent snow, rain, foreign substances, etc. from entering, so indoors would be more suitable than outdoors. However, while linseed oil is oxidized, a very strong odor is produced, so choose a well-ventilated and
sparsely populated room and manage it for a very long time and dry it.
1.2. Chemical Method
Linoxyn can be made in a very short time (about a week) by forcibly oxidizing using nitric acid or the like. However, since the chemicals used here, such as nitric acid, are very dangerous substances, in the case of Korea, where I live, the general public cannot even purchase them at all. Also, even if purchased, the working process is very dangerous, and even if you have successfully completed the working process and obtained Linoxyn, you cannot be assured about its purity. This is because the general public, who are not chemical experts, cannot be
relieved about the product manufactured using hazardous substances, and it is also accompanied by concerns about residual impurities.
2. Acceleration of Natural Drying
The oxidation reaction of linseed oil is, as the meaning of the word, reacts with oxygen. Therefore, oxygen is essential. In the early days of the invention of Linoxyn, it is said that Linoxyn was obtained by blowing hot air into a tank containing linseed oil for several hours and then cooling it. Anyway, to accelerate the reaction, allowing the linseed oil to meet more oxygen will be the most important accelerating method in the natural drying method.
Another factor that accelerates drying of linseed oil is UV light. This is why, when applying oil varnish, put the instrument in a UV-Box to dry it.
In conclusion, it can be said that the two factors that accelerate the oxidation reaction of linseed oil, namely, oxygen and ultraviolet rays, are the most important to accelerate natural drying.
2.1. Increased Oxygen Contact
There are two ways to increase the oxygen contact. One is to forcibly supply oxygen (air), and the other is to widen the area of the material in contact with oxygen. The first, forced supply of oxygen, can be realized by forcibly supplying air using a fan. Second, to increase the surface area of the linseed oil in contact with oxygen, this can be realized by placing the linseed oil in a low and wide tray and drying it. Also, in the case of liquid, it is often stirred so that it can contain a lot of air. After solidification, it is necessary to periodically pulverize it to break up the particles to maximize the contact area with air.
2.2. Increased UV contact
Exposure to natural light (sunshine) outdoors is not recommended due to the problem of foreign matter inclusion and the fact that the light does not last 24 hours. Most violin makers will have a UV-Box, so if you use it, you can stably supply UV rays indoors.
3. Experiment
3.1. Experiment environment
Let’s imagine an experimental environment that simultaneously satisfies the two conditions in the previous chapter.
In order to shorten the drying time as much as possible, use Boiled Linseed Oil, not Raw Linseed Oil. A UV-Box is used for UV supply. The UV lamp will be used as it is from the UV-Box that we currently have. To widen the area where oxygen meets, I decide to put the oil in a low and wide stainless steel tray. Next, for oxygen supply, a fan must be installed in the UV-Box for forced exhaust, and an air intake must be provided accordingly. An air filter is required at the air intake to prevent the ingress of foreign substances. However, in order to further increase the efficiency, it is decided to install a circulation fan to forcibly circulate the air in the box. That is, the internal air is discharged to the outside by the forced exhaust fan, and accordingly, the outside air enters through the air filter. The fresh air is strongly circulated in the box by the internal circulation fan and is discharged again by the exhaust fan. This process is continuously repeated. This is to ensure that a lot of oxygen is continuously supplied to the linseed oil by the air (wind) circulated strongly within the box. Additionally, the tray containing the oil must be rotated continuously for a uniform reaction.
Currently, the UV-Box that I have produced is fully equipped except for the fan for internal circulation. Therefore, only the fan for internal circulation is additionally installed and the experiment is carried out.
⃝ Material
• Boiled Linseed Oil 1L
⃝ UV-Box
• UV-Box internal volume : 60 * 60 * 156[cm]
• UV-A lamp : 40W * 1EA + 6W * 1EA
• UV-C lamp : 36W * 1EA + 6W * 1EA
• Exhaust fan : 18W
• Circulation fan : 18W
• Rotary motor : 1.2/min
• Others: Thermo-hygrometer, Air filter
⃝ Other equipment
• Stainless square tray(22*29*5[cm]) * 2EA
• Balance, Stainless steel rod, Scissors, Hand grinder, Tray shelf
Figure 1 is the UV-Box. Install a fan on the inner ceiling as in (a) so that the wind blows from top to bottom. (b) is a shelf on which a stainless steel tray filled with oil is to be placed. By placing a tray in the center of the shelf and placing an instrument on the top of the shelf, you can dry the instrument at the same time. The shelf is rotated by the rotating motor (rotating plate) under the tray shelf. There are main lamps in the corners and auxiliary lamps on the ceiling and floor, but the lamps on the floor are not used in this experiment. A thermo-hygrometer is installed on the UV-Box door to check the internal temperature and humidity without opening the door (c, d), and there are a number of holes and air filters at the bottom of the door. (e)
Figure 1: Inside of UV-Box
3.2. Experimental process
When the surface of the material starts to harden, it is periodically stirred with a stainless steel rod so that the material and oxygen can contact evenly. If the drying proceeds further and the entire material becomes sticky, air bubbles are generated inside the material by this stirring action, and these air bubbles allow contact with the air even inside the material. When it becomes semi-solid as it dries further, it becomes difficult to stir with the stainless steel rod, so cut it to an appropriate size with scissors to increase the surface area in contact with air.
When the stickiness has disappeared to a certain extent, use a hand grinder to crush it into small pieces to maximize the surface area in contact with the air. After that, at an appropriate time, use your hand or a strainer to periodically loosen the agglomerated grains. If you grind it with a hand grinder, the volume will increase a lot. One tray is not enough, so divide it into two trays and insert a wooden bar between the tray and the tray to stack the two trays up and put them on the shelf.
The completion time of the oxidation reaction is comprehensively judged by the change in weight, the presence or absence of odor, and the state of oiliness when touched.
3.3. Status by course
Table 1: Drying process of linseed oil
Figure 2: Drying (oxidation) process of linseed oil
4. Conclusions and considerations
The weight increased until 4 months, but after that, the weight decreased again and stabilized at 9 months. It increased slightly again at 10 months, but it seems reasonable to view it as an experimental error.
The stench generated during the reaction becomes stronger and weaker from the 6th month onwards, and at the 10th month, the stench is almost nonexistent and instead, a different characteristic odor is produced. At the 10th month, the granules stick a little, but fall off easily and there is no significant change thereafter. Therefore, it can be inferred that the reaction is almost complete at the 10th month.
In conclusion, it can be inferred that the reaction actively occurs with an increase in weight up to the first 4 months, and then the reaction is completed at about 10 months as the weight decreases again. The increase in weight at the beginning of the reaction is presumed to be due to the combination with oxygen, but the reason why the weight decreases again is currently unknown. [947g: 1030g: 997g = 100.0%: 108.8%: 105.3%], so the weight increased by about 9% and then decreased again, and the reaction was completed with an increase of about 5% compared to the initial weight. In the whole experiment for one year, assuming that the amount of material lost in the grinding/stirring process is about 5g, the final weight can be estimated as 1002g. This is an increase of about 5.9% compared to the original weight.
Although omitted in this report, there was no surface area change for about 40 days when the fan for internal circulation was not operated in a separate experiment. Compared with this fact, it is judged that increasing contact with air by forcibly circulating air has a very large effect. Also, considering that 1L of linseed oil was sufficiently dried in about 10 months, forced air circulation can be said to be a very important acceleration method.
As for the effect of UV rays, we can’t draw conclusions because we haven’t conducted comparative experiments yet.
If you divide the linseed oil into several trays and use a more powerful fan, the reaction time will be shorter.
Hello, wonderfull research! were you able to dissolve your linoxyn in alcohol ok?
Correction : * Figure2,(a) : 0 Day > 1 Day * Figure2,(b) : 1 Day > 15 Days