You really should tone your prints with some type of toner if your
selling them. Selenium is my choice but you can use Gold Protective
toner, or Brown toner to produce a  slight color change. Any of the
above.

   There are two reasons for toning, one is esthetic where the color
of the toner is approprate to the image; the other is to protect the
image against oxidation and sulfiding by atmospheric polutants. The
best toner for protecting the image is a polysulfide toner like Kodak
Brown Toner or Agfa Viradon. These toners convert part or all of the
silver image to silver sulfide, which is a very stable material. This
type of toner is advantageous because it tones all densities about
evenly so will provide protection even when the print is only lightly
toned. Kodak Rapid Selenium Toner was for many years the toner of
choice for protection of both film and print images. But, about fifteen
years ago it was discovered that some microfilm treated with it was
degrading. Research showed that the toner did not work quite the way it
had in the past. The reason is not known for certain but the behavior
has been established. So, the old recommendation of using KRST at 1:19
dilution for a few minutes is no longer the ideal choice for image
protection. Greater toning in a stronger dilution is a good protectant
but causes more color change. Where the change in color and density is
acceptable KRST at 1:9 or stronger is a perfectly good toner for both
image protection and color change. The color from KRST is somewhat
different from KBT or Viradon. For color change the choice is a matter
of the color desired.
   All sulfiding toners provide good image protection when the image
is fully toned but KBT and Viradon are the ones that work best for
partial toning.
   Gold toners change the image color toward blue. They are very good
image protectors but do tend to split tone. Their main drawback is
cost.
   Toners that use metallic substitution of the silver after bleaching
in a ferricyanide bath, like Iron Blue toner or Copper toner, are less
stable than the original silver image. They are useful for prints that
are not expected to have long lives. Some of these toners produce very
attractive effects. Nelson's Gold Toner, a sulfiding toner with Gold as
a color modifier (shifts the color toward red) is also capable of
archival protection.
  Proabably any print that is sold should be either toned in a
protective toner or treated with as stabilizing agent like Agfa Sistan.
Sistan is not as effective as proper toning but provides considerable
protection without changing the appearance of the image.
  There has been a great deal of research on the protection of
photographic images in the last twenty years and much of this is
available on the web.
  For general instructions on toning I strongly recommend _The
Photographer's Master Printing Course_ Tim Rudman  An Amazon search
will find it.

--
Richard Knoppow
Los Angeles, CA, USA
dickburk@ix.netcom.com

Just try. Your question will be solved. I always selenium tone FB prints,
not for permanence - I have no museum ambitions - but for depth of blacks
(Ilford Multigrade).

Jan