How to change the blade in an ancient knife

[amena]

I have often had to change the blade of an old knife. However, when most of the pitch (rosin? colofony? I don't know what it is called exactly) contained in the handle has been lost, I find it difficult to add new one, because the heat creates bubbles that cause most of the pitch to escape. Anyone know any tricks to change the blades in the best way?
Thanks
Amena

[AG2012]

Hi,
My experience with rosin (colophony).
Oven top temperature is too high because rosin boils and even explodes out of the handle.
Therefore, boiling water is more practical because the temperature of boiling water (although varies with different specimens), brings rosin to semi-fluid state.
Put knife handles in adequate pot (vertically),add water,when boiling and rosin semi-fluid,insert blades and manipulate using kitchen gloves.
Have seen gypsum plaster used - never do that.
Regards

[amena]

Hi
Thanks for your contribution
I also put the handle in boiling water, but evidently I do something wrong.
I fill the handle with powdered rosin and then I begin to heat slowly. However, when the rosin begins to melt, it becomes frothy and grows a lot, coming out. When I insert the blade, more rosin comes out and so, when it cools down, sometimes the blade is badly fixed.
How can swelling be avoided?
Regards
Amena

[AG2012]

Melt the powder in small vessel with the spout (e.g.coffee pot in the image) and while still semi-liquid,pour resin into handles which are held vertically in warm water.
If you melt the powder directly within the handles the rosin will behave exactly as you described.
Regards

[amena]

Great. Thanks for your advice.
I will try this method and let you know.
Best
Amena

[amena]

I honestly thought it was easier.
In fact I recycle the rosin that I recovered from cutlery that I melted, on the other hand I would not know where to buy new rosin.
This rosin is not homogeneous and with boiling water it becomes only creamy and it is not easy to pour it into the hole of the handle.
However, I tried another method to get the job done.
I used 7 mm diameter sticks of hot glue. I held the handle in a vise and heated it with the heat gun to the melting point of the glue, then pushed in a couple of sticks, until the handle was full.
I inserted the blade and waited for it to cool down. I removed the glue that had come out with a hard plastic spatula and cleaned the remaining traces with ethyl alcohol. For the moment the work seems to have been successful. I don't know if problems will arise in the future, but I don't think so.
Best
Amena

[AG2012]

Hi,
Enter into search engine
500g Natural ROSIN Pine Resin COLOPHONY Incense Solder Flux

Regards