This may be use full.
Thank you for the link Neil, looks very interesting.
De nada. It was for me and now I know why my plants have the unsaturated look. It also raised some Questions such as, for a 100lb. bag of 10-5-10 theres 75lbs. of undisclosed something. I found an old bag here touting the benefits of use that looks like cinders from a refinery stack without disclosing composition, which could be radio active for all I know.
Be happy.
In theory, Neil, it’s clay, but a good decade ago, I saw an article stating that the filler is unregulated and asserting that some unscrupulous chemical plants have supposedly been known to use mystery-filler as a means of getting rid of some unwanted stuff… Supposedly, the story goes, there was a farmer who could not determine why his crops began failing after several productive years, and ultimately found his soil had accumulated toxins – the source of which was eventually determined to be the filler in the fertilizer he had been using…
A quick google of the subject “toxins” and “fertilizer” yielded the link below, apparently confirming what I had read…
Link: community.seattletimes.nwsource.com/archive/?date=19970807&slug=2553534
lol at a place I used to work, one of the smaller farms had soil that was so salty from using nitrogen non-stop that the top layer of soil looked like Christmas. It was awful, lol. I’m guessing that amphibians or slugs didnt visit there much 
So it really doesnt even require toxins or fully knowing what is in a mix to ruin the soil. The usual culprit seems to either be laziness, greed or a complete bankruptcy of holism.
While there may be mystery stuff in cheap fertilizer, the label for NPK must always equal only a fraction of the total. That’s because the pure chemicals are not usable. Pure potassium generates hydrogen in presence of water, like sodium does. Pure N is a gas (N2) and is 80 % of the air, but not available to plants. White phosphorus is used in incendiary devices. So it always has to be a compound of something.
The purest you could get is something like ammonium phosphate and potassium nitrate, or urea. The ammonium phosphate is about 1/4 P, but by some odd convention the P is actually expressed as P2O5 so it is counted as considerably richer. The ammonium phosphate is also around 20 % N, or 10 % depending on which salt is used. The potassium nitrate is nearly 40 % K, but only 14 % N. Ammonium nitrate (banned now for its explosive properties) is nearer 1/3 N. Urea is about 48 % N.
So when you make a mix from these pure ingredients you will not get them to add up to 100 %. Something around 15-15-15 is the about best you could hope for. More of one means less of another. The high priced soluble fertilizers, are formulated with various combinations of these pure salts. Lawn fertilizers are a whole other thing.
Philip: That was a good link to read and then followed some others and some cases there was radioactive substances.
Larry, 30-30-30 is actually quite common, which doesn’t make a whole lot of sense to me. I’ve had such that still appeared to have a bit of clay in it.
Lately, I’ve tried to be more organic. Doing so aids microrrhizae, yields more stable/gradual nutrients, etc., but adds up in cost. Nonetheless, when I’m diligent about such, the results seem far superior.
I saw on=line that 20-20-20 by Peters is standard, but have not found anything higher in all 3 categories. Urea with tribasic potassium phosphate would be the highest you can get and I haven’t done the arithmetic on that. But the pH would be above 10.
BTW I was wrong on K, it is calculated as K2O which cheats just a little, but less than P2O5.
Lignin is used in the prilling process, to make the fertilizer into granules. Along with the clay diluent in the lawn stuff.