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When I was researching this topic I found only fragmented and inconsistent information, so I decided to create an end to end guide based on my experience.
What you need: bottle of baby oil and (old) rubber. You want a baby oil whose main ingredient is mineral oil or paraffin oil (they are the same thing). I chose Johnson's baby oil, whose ingredients are paraffinum liquidum, isopropyl palmitate and perfume. A quick search suggests the isopropyl palmitate is a thickening agent, that makes cosmetics feel soft and loook shiny. That's not desirable for our application, the active ingredient is the "liquid paraffin". I'm wondering if some of the thickening agent can be filtered out using something like a paper coffee filter or charcoal filter. Nivea also makes a mineral oil based baby oil. Many of the other baby oils sold in stores are based on seed or fruit (vegetable) oil. You don't want those.
The rubber I used was a Friendship New 729-02 Sensor, 2.2mm and 45° hardness (I think that's European, not DHS). It's about 6 months old, used and tested on a few different blades. That caused the rubber to be concave on the sponge side or "curve the wrong way" like some people say.
First application: when I removed the rubber from the blade, the glue stayed on the rubber. I applied the oil directly over it. The oil bottle has a nozzle, when you tip it 2-3 drops fall without needing to squeeze or shake it. I spread the oil with my fingers, adding more as needed to cover the rubber entirely. I didn't want to overdo it so I apllied the thinnest layer possible, just enough to cover the entire surface. The oil was absorbed quickly, in less than 5 minutes. I let it dry face up for 24h. After 24h there was no visible change, the rubber was still concave on the sponge side.
Second application: after 24h, I applied a new layer. This time I applied the oil more generously, but still not more than you would a thick coat of glue, distributing it evenly. It took a little longer to be absorbed, around 10 minutes. Because the sponge was concave, it was pooling a bit in the middle while the edges had already dried. I redistributed it to keep it even. I let it face up to dry, and after 1h the rubber had already flattened. After 24h it still looked flat when lying down, but when held vertically in the air it showed a little dome on the sponge side.
Third application: after another 24h, I applied another layer, about as thin as the first one. That seemed to strengthen the dome a little bit, but not by much. 24h later the dome is small when the rubber is lying down, and more visible when held vertically. When bent, the rubber feels relatively hard and and springy. For the purpose of my experiment that is enough. After letting it air another 24h, I glued it back on the racket. It is visible that the rubber has expanded in size side to side. When pressed with the fingers, it does not feel any different than before. A bounce test suggests it is a little bouncier than before. I am comparing it with the rubber on the other side, which is identical but in 42° so normally bouncier. The tuned rubber now has the advantage.
I tested the tuned rubber in training for 30-40 minutes last night. I did not feel any change in trajectory or anything out of place. It spins the ball well. My forehand is pretty strong so it's hard to say if I felt a speed increase. It would have to be a considerable one to feel it. Overall I am happy with the results.
Conclusions:
- Thin layers don't seem to do much, next time I will apply thicker layers like #2 from the beginning. Two thick layers should be enough to give you a dome, a third one of varied thickness can be used optionally to achieve the desired result.
- The rubber behavior is pretty predictable based on the thickness of the oil layer, and most of the change happens in the first hour
- I would recommend one layer to anyone with a concave rubber to make it flat. It will be easier to glue and potentially giving you a tiny bit increase in performance.
Picture 1: Before #1 layer, the sponge is concave (edges raised in the air)
Picture 2: 24h after #2 layer the sponge is flat viewed from the side
Picture 3: 24h after #3 layer the sponge has a slight dome viewed from the side
Picture 4,5: the sponge shows a stronger dome when held vertically in the air
Julian
What you need: bottle of baby oil and (old) rubber. You want a baby oil whose main ingredient is mineral oil or paraffin oil (they are the same thing). I chose Johnson's baby oil, whose ingredients are paraffinum liquidum, isopropyl palmitate and perfume. A quick search suggests the isopropyl palmitate is a thickening agent, that makes cosmetics feel soft and loook shiny. That's not desirable for our application, the active ingredient is the "liquid paraffin". I'm wondering if some of the thickening agent can be filtered out using something like a paper coffee filter or charcoal filter. Nivea also makes a mineral oil based baby oil. Many of the other baby oils sold in stores are based on seed or fruit (vegetable) oil. You don't want those.
The rubber I used was a Friendship New 729-02 Sensor, 2.2mm and 45° hardness (I think that's European, not DHS). It's about 6 months old, used and tested on a few different blades. That caused the rubber to be concave on the sponge side or "curve the wrong way" like some people say.
First application: when I removed the rubber from the blade, the glue stayed on the rubber. I applied the oil directly over it. The oil bottle has a nozzle, when you tip it 2-3 drops fall without needing to squeeze or shake it. I spread the oil with my fingers, adding more as needed to cover the rubber entirely. I didn't want to overdo it so I apllied the thinnest layer possible, just enough to cover the entire surface. The oil was absorbed quickly, in less than 5 minutes. I let it dry face up for 24h. After 24h there was no visible change, the rubber was still concave on the sponge side.
Second application: after 24h, I applied a new layer. This time I applied the oil more generously, but still not more than you would a thick coat of glue, distributing it evenly. It took a little longer to be absorbed, around 10 minutes. Because the sponge was concave, it was pooling a bit in the middle while the edges had already dried. I redistributed it to keep it even. I let it face up to dry, and after 1h the rubber had already flattened. After 24h it still looked flat when lying down, but when held vertically in the air it showed a little dome on the sponge side.
Third application: after another 24h, I applied another layer, about as thin as the first one. That seemed to strengthen the dome a little bit, but not by much. 24h later the dome is small when the rubber is lying down, and more visible when held vertically. When bent, the rubber feels relatively hard and and springy. For the purpose of my experiment that is enough. After letting it air another 24h, I glued it back on the racket. It is visible that the rubber has expanded in size side to side. When pressed with the fingers, it does not feel any different than before. A bounce test suggests it is a little bouncier than before. I am comparing it with the rubber on the other side, which is identical but in 42° so normally bouncier. The tuned rubber now has the advantage.
I tested the tuned rubber in training for 30-40 minutes last night. I did not feel any change in trajectory or anything out of place. It spins the ball well. My forehand is pretty strong so it's hard to say if I felt a speed increase. It would have to be a considerable one to feel it. Overall I am happy with the results.
Conclusions:
- Thin layers don't seem to do much, next time I will apply thicker layers like #2 from the beginning. Two thick layers should be enough to give you a dome, a third one of varied thickness can be used optionally to achieve the desired result.
- The rubber behavior is pretty predictable based on the thickness of the oil layer, and most of the change happens in the first hour
- I would recommend one layer to anyone with a concave rubber to make it flat. It will be easier to glue and potentially giving you a tiny bit increase in performance.
Picture 1: Before #1 layer, the sponge is concave (edges raised in the air)
Picture 2: 24h after #2 layer the sponge is flat viewed from the side
Picture 3: 24h after #3 layer the sponge has a slight dome viewed from the side
Picture 4,5: the sponge shows a stronger dome when held vertically in the air
Julian
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