I heard from another modeler that George Aldrich used Knox gelatin powder in clear dope to seal balsa. Anyone know about this and how well does it work?
        Doug

I've heard of using gelatin powder in the water for wet covering with silk.  Idea is to partially close the holes in the weave, and not have dope penetrate. I've never tried it. 

Probably the safest and best way to preseal silk is to first cover the wing with tissue.  Apply a couple coats of dope, and then apply the silk.  The tissue seals quickly and prevents the dope from dripping through the silk.  Ty has the easiest idea.  Once the silk is sealed 6-8 coats of dope will completely fill almost any fabric.  Sand it down until the fabric grain disappears and you can get a very, very smooth surface.

I haven't used gelatin,  but from a chemistry standpoint here are some tips:
Gelatin won't dissolve in dope.  It dissolves in water.  Mixing the two will make a lousy mess.

Dissolve gelatin by first putting a couple packets into 1/2 cup of cold water.  Stir it in briskly with a fork or whisk and let it sit.  The gelatin will soak up most of the water and get sticky.  Gently warm it in a pan until it liquifies.  Add more water to get 1 cup per packet used.  Knox gelatin will gel about one cup of water per packet.  Keep it warm.  If it cools it will get thick and hard to apply. 

Use it only on fabric, silk, etc. to fill the gaps.  Don't bother with it on silkspan.  3 coats of dope will seal silkspan faster and easier.  Make up a couple of test panels.  Do the first with 1 cup of water per packet.  Then thin it to 2 cups per packet for the second panel.  When they both are dry examine them closely and figure out which way to go- more or less gelatin to water.  You want just enough to fill all the pinholes in the silk.

When the silk has been applied, shrunk, and dried apply a thin coat of the gelatin solution.  Try not to push it through the silk, that just adds weight.  Let it dry thoroughly.  Look closely at the surface to see if any pinholes are left.  Touch up and let it dry again before sanding and doping.

  Yeah Doug, looks like my "memory" is going bad, or WORSE..My Bad...

I used Knox gelatin/water to apply silk to a couple of planes I built when we lived in the desert (Edwards AFB). It worked fine, except where I got a bit overzealous and slopped some gelatin onto the silk at the edge of an open bay...wrinkled there. Both planes. The woodwork where the silk was applied with the gelatin was nicely sealed and shiny with a just few coats of dope.

All that aside, I'll probably never use silk again, and I think I'd rather use corn starch or Zinc Stearate.  Steve