Soldering silver work into gold?

hi folks I’m attempting to make the transition from silver work into
gold and have been enjoying the discussion on retipping rings.
Several posters recommended to be sure to use actual material as
opposed to just using solder as the solder would not be as strong and
soon wear away. It got me to thinking, isn’t solder actual material
in itself, whats the difference?; just a tad lower in karat. I
realize that this is more theoretical than practical understanding
but what is the difference between using so me 12k solder or some 12k
wire to retip; or any other fabricating technique for that matter.
I’m very interested in making the move to working more so in gold as
opposed to silver and am open to any hints, translations , tips or
pointers. I’m fairly comfortable with sterling techniques,
fabrication and casting ,and would like to covert these skill into
gold work. Thus far I’ve only done a few 14k ear wires and
bezels. Thanks as always . @mark_kaplan