OK, Aelia, here you go - pictures of cartoneria! The complete process is not documented (maybe later) but here is enough to get an idea of the process. It's a pretty cheap project: old newspaper, grocery bags, bailing wire, flour and water cost practically nothing. The only supplies that cost any money were the acrylic paints and gesso.
First, make desired shapes out of crumpled newspaper and masking tape. If items will be strung together or have wire in them for support put them in at this stage. Trying to do it later is very difficult.
Next, make the paste. Here I put 3 tablespoons of flour into 2 cups water and stirred thoroughly, getting out all the lumps. Then I put the pot on high heat and cooked, stirring constantly, until the mixture began to bubble gently. I then poured it into a bowl and waited for it to cool off enough to handle with my fingers. The glue is most pleasant to work with when it is still warm, so it's best to make it right before use.
Wet torn newspaper, glued in four layers, is torn into smaller bits and applied to the newspaper and tape base. Here is a crown of lilies in progress:
and a pile of bones and a dragonfly:
After the newspaper dries, apply a layer of brown paper (grocery bags or cement bags work well). These are two stylized skulls and a rose:
After the brown paper dries a layer of gesso is applied. Then the items are painted. The gesso and acrylic paint I used was cheap stuff because I am making a lot of items. The low quality paint really makes a difference but that much good quality paint would be very expensive! I used an off-white color for the bones because plain white just didn't look right. The items in this picture are skeleton parts mostly and they're not all quite finished with painting.