I found that to be the case many years ago, perhaps its unwritten because
so many people have tried it, it has become an unspoken "given"
never the less its a fun experiment. And if edge to edge sharpness is not the
goal, then perhaps it suits the purpose well.

A paper negative will never be as sharp: the light making the exposure
is _very_ diffuse with the paper base acting as a diffuser.

The image will undercut (called 'choke' in the graphic arts industry)
from light penetrating into the paper at an extreme angle - flying
low under the cloud cover of the negative, as it were.

The graphic arts industry uses a diffusion screen (sometimes called
a 'diffusion foil'), made from a sheet of matte drafting mylar (think
onion skin paper) that is placed just above the contacting print frame.
In this instance it is used to shrink the size of lithographic dots and
to produce fancy graphic effects on lithographic film.

The fuzziness, however, should be uniform across the paper.  Variable
fuzz is an indication of bad contact.

Try a real contact printing frame.  After that, the next step is a
vacuum printing frame: this is made from a plate of glass and a rubber
blanket, the materials are placed between the glass and the blanket,
the frame is closed up and the air is evacuated between the blanket and
the glass - this results in 14 lbs/in^2 clamping force, or about 1/2
a ton for an 8x10 print.  Even with this force (an also because of it) it
is very hard to get all the air out, a pressure gradient is required to
get airbubbles to evacuate.

My partner and I were the inventors of Nuarc's nuVac vacuum frame
contacting system, U.S. Patent No. 4,935,773.

 I've never heard it mentioned that it is possible to do so. There is
an article by Liam Lawless at Unblinking Eye which describes a direct
negative method for doing so.
 I've the method in mind for future trial. The method allows for some
adjustment to the original. That will help render some of my not so
photogenic vistas more printable.
 In fact the direct negative approach may have me buying or
constructing some contact printing frames.                         Dan

Hi

There is really no need to contact print paper negs.

I use 8x10 Color RC paper as negative material in my pinhole camera.  After
typical 2 minute sunlight exposure using an 85B filter, I process as usual in a
roll transport processor.  

Then I scan the color paper negative on a Epson scanner.  Then use photoshop to
reverse the image and color correct.  I print the results out on 8x10 color
dyesub paper.

The results look just great and sharp.

Larry