I placed 1.5K or Seville oranges in a large jam kettle ( a thick bottomed large wide saucepan), some recipes say halve the oranges, bugger that, just put em in. I scarred the skins with a sharp knife, to allow the oils and flavours to seep into the water more easily.
I brought them to the boil for about ten minutes, and turned off the heat, and let it stand for about 2 hours, whilst I made a nice cup of tea.
Using a scoop to take the oranges out of the jam kettle.
Then I took the oranges out, put them in a colander over a bowl, to let the juices drip out,
and chopped them in half.
once they were all cut in half, I put a muslin cloth over a bowl, ready for the next step.
Using a spoon, I spooned out the insides which I placed in the muslin cloth I'd placed over a bowl.
When I'd finished scooping the insides out, I tied the muslin cloth and placed it in the Jam Kettle, ( large saucepan in case you forgot)
The insides, or pith, and seeds are where all the essential pectin is stored, and the cloth ensures it doesn't make the marmalade creamy coloured, and mushy, whilst letting the pectin through. 
before getting my fingers covered in Orange juice. chopping time!!
I chopped up the orange skin, I chopped larger slices, cause thats the way , aha aha I like it.
(chop them to whatever size you prefer in your marmalade.)
Because the oranges had been simmering for about 2 hours, some of the water will have evaporated, so add some more to bring it up to the same level as before.
Then I brought it to the boil for 15 mins,
Then I lowered the heat and simmered the lot for about and hour and a half.
Oh I also added two lemons, I forgot to tell you that.I squeezed all the juices out of the muslin cloth using a wooden spoon in the colander. as it was too hot to use my hands.
Then when the liquid was reduced by about half, I took out the muslin bag, squeezed all the juice back in the pan. there's all the extracted pectin, so now its all ready and looking a nice orangey colour ready for thickening.
Then I added about 2.5k of sugar. Due to the high pectin content, you don't need to buy special jam sugar, any sugar will do, I used normal white granulated. Also sugar content depends on how sweet you like your marmalade darlings.
If you prefer a dark marmalade, use a dark sugar, simple isn't it.
Here's the fun bit, nearly all recipes online read " Bring it to the boil and boil rapidly for 15min or until setting point is reached " What??? setting point, whats that...
Its simple, once the pectin has been activated by the heat, it will start to thicken the mix, but its hard to tell when its hot.
So this is what you do..
After about 15 mins, take a spoonful of the liquidy marmalade, and tip it on a cold plate or saucer. then after a couple of minutes when its cooled, run your finger along it and it it wrinkles up, its ready, if it doesn't, boil it some more.
from here on it its test test test..
if you boil it too much your marmalade will thicken so much when it cools you won't get a knife in it, so you'll need to put the lot back in the pan and water it down.
OK where was I? Oh yes.
Jam jars ( preserving jars)
I saved loads of jars during the autumn from jam and all sorts of things,
Wash them, sterilise them (boiling water is good for that) whats the point in buying jam jars when you must have some in the house, well I did.
Then pour in the liquid marmalade into each jar.
I filled them to the top and put a little paper disk on top.
those you can get from catering shops or supermarkets etc. they seal the top so no oxygen comes into contact with the marmalade, which could cause mould to grow.
Put the lids on, and there you go Marmalade a la Seville!!
Oh make some toast, butter it, then be the first kid on your block to taste the fantastic Seville marmalade.
Like me you will end up giving some away to freinds. they will love you for it, Honest.!