I’ve actually had the exact same issue on some wrought iron. Would love to see an explanation on this

Without actually seeing the issue I will ask this- are you welding with or without flux?   Is the area rough to the touch, i.e. would you feel drag if you wiped the area with a cloth?  Are the edges regular or irregular? 

Thanks for your reply, Kevin. I tried to attach a picture earlier but it got kicked back because it was too big. I think this smaller version will show up. Yes I did use borax for flux and the portion that rejects the etch is too small for me to feel, but the flawed parts almost look like the surface of sandpaper. The problem seems to be with the 1095 layers but not the 15N20

The reason for my questions was that your description sounds like what I used to call "white inclusions" 

My metallographic studies of it show a combination of scale and flux get captured between layers, reducing down into a silvery oxide that is very, unevenly, prone to attack by the etchant.  If you ever get a "blister" in a billet, you will probably have this issue where the blister was.  Some may be quick to blame flux these days but it is more an issue of surface prep.  Any deviation in the surface that could trap gas, oxide or flux could cause this. A truly flat surface, even with moderate grinder scratches has no place to trap material and will avoid this.  Very thin steel, even if ground flat, in a large welded stack also likes to cup when heating up and create this issue, I have never got it when using thicker, well ground, layers. 

It does not have the appearance of post welding decarb which would be smoother looking and a bit more uniform, but I considered the possibility from your original description. 

Thanks, I can go along with that. This billet was one that I had stacked 4 together in a square formation. they were not quite straight and I just heated it up to welding heat and counted on the press to smash everything together. I't easy to suppose that I got some flux trapped in there. If I don't get everything perfectly flat do you suppose I could solve the problem by using kerosene when I weld it? Otherwise I guess I just have to cool everything down and work it flat.

I have had this on a couple blades as well and have been able to sand past this.  My suspicion has been that it is from my tack welds.  I try and always grind away my welds after I am done setting and after a few presses.  however, I am thinking that I manage to get a bit of weld steel into the billet.

The spots always show up about where my mid stack weld would be, thus my reasoning that it is my tack welds. (that plus I am a crappy welder)

Going on Kevin's answer, I'll assume that the flux is trapped between two layers. I have a little bit of margin here so I ground the affected blade down past the layer that was showing. We'll see how it etches and I'll pass it along.

I have had this in the past as wel. It has always been in a spot where scale was present. Usually on the flats of the blade where I didn't grind much deeper after forging or heat treat. I have noticed a coffee darkening will Usually darkening those spots. Usually I try and grind them out tho.