Acronyms are great, are they not? I can now talk all day about ASOs without you even knowing what I am talking about. Yet, I will elucidate. ASO stands for Anvil-Shaped-Object. These are cheap cast iron anvils no better for forging than they are for effectively hitting a speeding road-runner.
What does an ASO look like?
First, recognize its shape. Castings are blocky and do not possess the grace and finesse that real forged or cast steel anvils do.
A duck in all respects but the quack, this 55lb ASO from the box store is a piece of junk. See the casting line? Also, look for the lack of a faceplate.
Another great ASO. This one has a good conical horn, but still has the ugly casting marks, and doesn't even look like an anvil. Avoid it.
Can you tell? Avoid these.
This one may well be a good brand of cast Steel anvils, I don't know. Just look at the raised letters and numbers: Only in cast anvils (iron and steel) can you find these raised markings.
This one says "John Deere" on it. It is cast, as a paperweight.
So, there are cast steel anvils out there. If in doubt, go to Iforgeiron.com and check it out. Also, check the rebound with a steel ball bearing. 80% rebound is good, also, check for some type of ring. There also have been anvils that are cast with steel plates in them, such as Fisher anvils. Therefore, unless it looks like a cast iron ASO, check with a professional.
As always, hammer happy.