Help - Doubling up necklace chains

[xblackxstarx]

hello everyone
I have a Tiffany’s necklace which won’t come off it’s chain and I would like to extend the chain . I noticed they sell a 36 inch delicate chain on their website so I was wondering if it would be the same as simply adding two of my 18 inch gold chains together or would this not be as strong and more likely to break than a 36 inch chain.
The reason I’m doing it this way is that I can’t go into a Tiffany store to have it extended and I’m not comfortable sending it through the post either . I thought about attaching a bracelet like the DBTY bracelet to extend it by 7iches too.
Has anyone ever done this with a delicate chain ?
Do you think a 36 inch chain can last being so delicate ? They sell it as a 36 inch delicate chain so I don’t see why two 18inch chains wouldn’t work
Opinions and experiences welcome here id love to hear everyone’s thoughts on this
I will attach photos of the chain

 

[xblackxstarx]

Why has this thread been moved ??? I posted it in the general jewellery section as this isn’t about the brand name but about attaching two separate chains together .
The examples I’m using are Tiffany but it’s not about the brand it’s abour whether attaching two fine 18 inch chains together is going to be as strong as an individual 36 inch chain .

 

[xblackxstarx]

It’s a general jewellery question non specific to the brand at all.
I’m more likely to find others who have relevant advice in the other section