Bullet Proof Negative, or How I Almost Lost It...

I need to vent, so here it goes:

Today, of all days, I decided to finally print that 20 year-old "bullet-proof" negative (calling it "very dense", simply would no do it justice). I knew this negative would be the mother of dense negatives the split second after I exposed it but it was too late and it's a whole other story.
It is a photograph of a dear family friend and when I visited her she had just turned 99. I am currently printing for my family album and she has to be a part of it. This was the best shot I had of her as far as "image aesthetics" go.
My normal set-up is a Durst Multigraph with an 80mm f5.6 lens, and a glass negative carrier (w/anti-newton glass).
The contrast filter reading said 4.4 and the exposure somewhere at 90 secs. and f5.6
So I changed the lens to a 50mm Nikkor f4 in order to bring the enlarger's head closer to the baseboard (more light intensity). I almost forgot: the enlargement is 5x7 of the full-frame negative. There is so little room for my head and the grain focuser that I start muttering to myself.
First strip test at 60 secs. and f4 is 20% too light, so I add 20%. Looks good: I expose the whole sheet and when I finally turn on the lights what do I see? Some weird mesh-like pattern over some parts of the image: it looks like mushy fingerprints. I clean the negative carrier, check it with a loupe and it looks good. Another print and another mushy pattern appears but not in the same area. I remember about the 2E filter above the light mixing box: I remove it even though it looks clean. Another ruined print. Now I am talking out lout to myself. I remove the negative carrier, remove the glass from it and insert the metal cut-outs for 35mm. Another print, mushiness is gone! but more strips are required because the exposure has changed by removing the glass. Tomorrow, if the gods of darkroom are with me, I will finish printing my "bullet-proof" negative.
Good grief!

It looks like you had Newton rings with your glass carrier. The shiny surface of glass cause these, that's why neg carriers use a frosty-looking kind (aptly named "anti-Newton").

Definitely Newton's rings. Newton's rings are caused by the interference pattern of light reflected between the film and the glass surfaces.

The best way to avoid this is with anti-Newton or anti-reflective glass on top of the neg carrier. You can use plain glass on the emulsion side. The anti-Newton glass may be textured or it may have an anti-reflective coating, like lenses have. If the glass in your neg carrier is the original glass from the manufacturer and no surface is obviously textured, it may already be anti-reflective glass, but you might have the glass reversed.

There are other methods, like giving the base side of the film a light dusting with cornstarch.

Films that have retouching surfaces on both sides (usually only medium and large format) tend not to have problems with Newton's rings.

Day Two.

I am now talking a short break from printing. This morning I did new test prints at different exposures without the glass negative carrier. Same mushy stuff on the normal to overexposed tests. It had to be the negative. I borrowed a high magnification loupe and the negative revealed splotches of varying "intensity". I used some emulsion cleaner and was able to remove most of the gunk. It now prints clean for a proper exposure.
What a ridiculous ordeal!
In hindsight, I should have taken a more magnified view of the negative. The glass negative carrier that I use has the anti-newton glass and was never the cause of such problems, even with 4x5 negatives.
Live and learn.

What a frustration. You never know, sometimes.

My mother told me there'd be days like this !!