I was at a tannk maker's place today trying to get a custom tank made. All went well until i mentioned using black silicon. He said that black silicon fails quicker than clear as the black is just the clear with other stuff added slit doesn't bond as well. He claims that tank built to the same specs in black and clear, the seams of the black always fail earlier.
I would assume he has clear in stock and rather than add more overhead to create your tank, he would prefer to talk you out of black. My tanks have black silicone. I have no Idea at the truth but it sounds like hogwash.
I suspect that the guy is right. Silicone is clear, so the only way to make it black is with a pigment, and that pigment isn't likely to make the silicone stronger, either in bond strength or tensile strength. But, as Wasserpest noted, that might reduce the life of the silicone joints from 100 years to 90 years. In any case I would bet that there is data available on what the comparison in strength is.
I'm going to have to go with Hoppy on this one. The majority of Perfecto/Marineland tanks have used black silicone for a while, and we've not heard of massive failures left and right so it cannot be a difference of "tank fails in 90 years vs 10"
I'm not versed in how black silicone is made, but the most common additive for making a plastic black is using carbon black, which is a fancy word for ash or soot. Adding it will increase the strength and stiffness of silicone, and would also improve resistance to UV degradation if silicone didn't already have high resistance. I couldn't find any drawbacks to using the stuff other than a loss of transparency. Perhaps it doesn't flow as easily since it is stiffer?
Normally I agree with Hoppy, and I guess I do here as well, but seriously... if you want black silicone, get black silicone. If the guy can't do it in black than he can't do it in clear either.
A high-strength, acetoxy silicone sealant providing outstanding adhesion and long-term performance for use in a wide variety of structural glazing and general glazing applications.
Joint Movement Capability (ASTM C719)- +/- 25%
Ultimate Elongation- 513%
Ultimate Tensile Strength- 480 psi (3.31 MPa)
VOC- 23 g/L
Work Life (tooling time)- 5-10 minutes
Food Contact- See data sheet
The info says nothing about differing tensile strengths between black, clear or white.
*Double post but my first reply failed so I did rewrite my post...
Same tensile strength in every colour, so there should be no issue. Normally I don't disagree with Hoppy, but if you are willing to trust silicone to hold together an aquarium (a completely ridiculous application for silicone) than trust the black as well. If your builder won't do it find another.
It's like not using crest because of the blue stripe, yet you'll use colgate.
Actually, I can see the black silicone lasting longer than clear, for no other reason than it is opaque, IE stops UV light damage past the surface. At any rate, the amount of lampblack (carbon) they would add to a tube of silicone to make it black would be less than a gram. I could see an additive making the silicone stronger in some situations if you used chopped carbon fiber. Although that might end up greyish black