Do the large Urns seep while the smaller ones don't?

Who knows.... we dont really have enough evidence or clues to see if there is any difference i would assume they would all activate in the same way?

But we cant rule out that size does make a difference to how fast they release their Agent...

I do wander why they never stuck to them having a uniform size for those Urns.... so yes different sizes does raise a Question Why?

The other one is why the writing is different to the Engineers

@Big Dave

Yea, I really think there may be a difference in the two sizes...aaahhhhh so many questions lol

I do have a feeling we might see how these babies are produced...maybe that will be the disaster scene...who knows..

the inner guts of the ern resemble kinda the insides of a missle...so strange the mechanics, and the fact that its alive is crazy...

There don't appear to be any urns that aren't seeping in the later scenes with Millburn and Fifield and when they find Millburn's body.

@S.M yea i noticed that, good point

Indeed internally they are set up like a conventional Weapon Warhead...

There are multiple levels/elements involved.... and a reaction must be needed to start the process, it would seem the Green Vials/Ampoules contain a chemical/substance and on the outside we have the Thick Black Slime and it would be logical to assume the changes in atmosphere/environment either

1) Cause the Black Slime to react and then eat through the Glass Vials mixing the substance inside to cause a violent reaction.

2) The Glass Vials react and melt/break down allowing the substance inside to mix with the Black Slime and cause a violent reaction.

I would say the internal substance is what holds the DNA related to the Xenomorph or contains a Parasite.

The internal workings of the Urns is very different to the Sacrificial Goo which looks like a substance that had Metallic Hues to it... starts off like a Chocolate Mousse or Frozen Mousse consistency that soon starts to Melt like Butter/Ice cream does when exposed to the Air.

Neither the external Black Slime of the Urns that are inside the Urn or the Internal Substance within the Ampoule Vials look like the Sacrificial Substance.

Off course in the concept work as shown in the Original Post the Black Slime (was green in some trailers) appears to be a Wax Like Substance in the Concept Work.

The Art of Prometheus book had a lot of interesting concept works and information but Sadly it was all only in French...

If there was a English version i would be interested in purchasing it and reading it.

I think the Urns in the Juggernaut(s) were fully weaponized, stored properly, and hadn't been triggered yet - but I'm not exactly sure what triggers them.  Like BigDave is saying, I think something the humans do changes the environment around the Urns and triggers the Urns to activate. 

The Goo would remain in a state of stasis until the container starts to rapidly break down and deteriorate. 

David applies some sort of chemical preservative to the outside of the Urn that he takes back to the ship to keep the Urn in stasis.  Which is what prevents that Urn from leaking.  The molecular bonds that hold the Urns together have already been breaking down under the surface for the last 2000 years or so, so the introduction of "fresh air" into the room is a large part of what causes them to rapidly distintegrate...  the material that comprises the Urns probably hasn't reached its half-life yet, so after it starts to decay, over half the material remains.  The Urns aren't able to fossilize, or enter a "miraculous state of preservation" in some other way; therefore, as soon as environmental conditions change, the casings of the Urns begin to rapidly deteriorate/disintegrate.

The radiocarbon dating performed on the Engineer head/body places it at approx. 2000 years BPD (give or take 100-150 years).  It's probable that the Urns in the chamber are from within the same timeframe, yet we don’t know exactly how old the temple/chamber itself is - or how long the temple’s been in use/occupied.  It’s difficult to assign absolute dates to some stuff, and there just isn’t enough contextual/environmental data to help calibrate, so it may be more useful to use relative dating techniques.  Under the surface, carbon elements in the bones were being replaced with other carbon elements leeched from sediments and rock in the soil and immediate surroundings.  The Engineer bones were fossilizing.  Weyland-Yutani doesn't know how or why this happens, because it's actually pretty rare that things turn to stone and end up entering the archaeological record at all.  It's almost a miracle that the head was so well-preserved inside the helmet.

The Urns in the chamber might actually be a little older than the dead Engineers and the Urns on the ships, because those Urns may have been sitting there for a while before the Engineer was decapitated.  If David drops one of the fully weaponized urns he's carrying into the Engineer home planet's ocean, then the container will begin to degrade, the chemicals will leak into the planetary water supply, and it will basically be Game Over for most forms of life on the planet.

As soon as the Accelerant and Mutagen combine with the ocean's biomagnification effect, entire biospheres can be wiped clean of complex forms of life with the weaponized Alien DNA.  David would basically be carrying hell with him inside his juggernaut.  If he drops the Urns into the water, then any living creatures on the planet might be doomed, or petrified.

Most organic matter will eventually decay and disintegrate, but Stone can last millions of years if there's not much erosion or weathering going on.  Certain metals will oxidize/rust and begin to break down faster than others, while wood needs to be petrified to be preserved.  Which may influence the Engineers/Builders to build most of their structures and statues out of rock/stone instead of metals.  Humans sort of moved away from working with Stone, but Holloway initially wanted to know if the temple was a natural formation (which had been carved out of a mountain), or if it was built by the Engineers.  Upon entering the temple, it becomes clear how the tomb was constructed - but it's never brought up again.  Holloway doesn't really document any of his findings before he dies; whereas, Shaw actually logs some of her observations. 

While Shaw and Holloway were busy getting busy, Dr. Ford was busy logging her own observations on the Engineers and Goo.  The Company has Dr. Ford to thank for transmitting all available data from the Prometheus mission to them, thus her immediate family has been compensated for Ford's full cooperation with company interests.  The insurance policy in her contract was paid out in full.  When Shaw is unconscious, David and Dr. Ford begin gathering data on the thing growing inside her:  Ford was able to get a quick look at the creature that was removed from Shaw while it was trapped in the room.  She was secretly able to transmit all the data to the Company before going to meet the Engineer.  After that point, Ford's data tranmissions stop.  The Company can't access the rest of her shoulder cam data to connect data points together.

"It's almost a miracle that the head was so well-preserved inside the helmet"

Indeed.... the environment may have been some kind of Safe-Zone... Quarantine and this room was able to be kept in some state that not only dis activated the Black Goo or made it unable to operate....  It also kept the Head intact..

David freezes the Urn and then Stores it in a Cold-Store Environment and so the Sealed Big Head Room must have been also a Cold Environment and also free from Atmospheric Elements that can have a effect on Genetic Material being able to degrade or multiply.

As far as the dates.... we dont know the full story of LV-223 and was it always a Bio-Weapons Facility

The Cave Painting in the Isle of Skye was dated as 35'000 years old....

How did this painting get there?  We have to assume via Engineer and Mankind interaction and so the Outpost LV-223 had been established at least 35'000 years ago.

However we dont know if the outpost was being used as a Bio-Weapons Facility maybe not as far as the Black Goo Urns found in Prometheus.   We have to ask if these Engineers had been working on such a Weapon 35'000 years ago then how come it had taken so long to Perfect until the Weapon Experiments got out of hand some 33'000 years latter (2000 years ago?)

If the Bio-Weapon was around 35'000 years ago then why wait all that long to attempt to use it?  And why visit us over and over generation in the future at different periods of Ancient Mankind Evolution?

I wander if LV-223 had a other intention, before some point it was then turned into a place to produce a Evil-Bio weapon or Upgrade.

Also the Urns or at least the Top Part seem to be made from a Material that can be directly effected by Environment and the Reaction of the Black Goo Bio Weapon inside.

Maybe they are simply made out of different materials? Compare it to how you make different kind of bombs and how the react (in a chemical way). This could make sense if we look at the urns and the monsters as weapons.