Here is a glass guide that I found on another forum. This guide will give you information about the basics of glass. Not all of this will apply to HydraTubes but the Cloud will work with any of the pieces described in the following guide...
The Glass Purchasing Guide
-The very basics: filtration, smoke volume, drag/turbulence.
In my opinion these are the three basic features of a piece that effect how enjoyable/smooth the smoke is. How much filtration, how much volume, and how much drag is acceptable is personal preference of course but these factors will always have significant impact. The more water the smoke has to flow through, the smoother the smoke. Water to smoke surface area contact removes the aqueous components from the marijuana smoke thus making it smoother and healthier than direct combustion. Smoke volume is fairly obvious, there is a certain volume of smoke that each individual can comfortably inhale and exhale without a dying cough.
Drag/turbulence play a role while inhaling to burn the bowl and when clearing. Too much drag when milking could lead to embarrassing drool and if there's drag when clearing, it increases the time the smoke is exposed to air (making it harsher and stale) and increasing the amount of time the smoke comes in contact with the lungs (longer delay would make it more irritable to the lungs)
-Know origin of production
This is not to say that the country of origin has a direct impact on the quality of the piece, however certain countries have reputation for better quality control than others and this seems to hold true majority of the time. The three main countries relevant in this discussion are China, Germany, and the USA.
China is the king of mass production, and pieces originating from China are just that, mass produced glass products. This is particularly not well suited for glass piece production. With the fragility of glass and all the removable components that must fit in joints with little tolerance, the quality control applied by the manufacturer are usually sub par, delivering products that can break easily or perform poorly. This is not to say that all pieces from China are weak and poorly produced, but one should keep in mind the production process that leads to the final product. Ive owned China glass that were free of imperfections and performed wonderfully; it is just up to the purchasing individual to apply his/her own strict quality control standards, which is why Ive attempted to create this guide.
I dont want to start a debate between Germany vs. USA (this really applies only to the ROOR brand) but the general consensus seems that products originating from these two countries have better quality control than China. That said, I have seen pieces from the USA that were produced poorly, so country of origin is never an end-all mark of quality.
-Know artist/company who produced the piece
-Brand and artist reputation isnt everything, but very important. Dont purchase a piece with bad reputation hoping that youll be the exception. I personally like to try to support local glassblowers who truly view pieces as art and not just glass to make money
-Straight Tube vs. Beaker:
The physical differences between the two are pretty obvious; one is a straight cylindrical tube whereas the other has a flask bottom base. Due to the streamlined design of straight tubes, they will always clear faster than their beaker counterparts. One thing to look for in straight tubes is the thickness and diameter of the base, as this translates to its stability. Tubes are generally more durable than beakers because of their design (a bump usually will contact the base vs. the beaker which can shatter). Some companies blow out the beaker straight from the tube and causes paper thin bottoms. Keep an eye out for beaker bottom thickness as well as tube thickness.
-Thickness of glass
Check the thickness of the glass to see how durable it is. Pieces usually range from about 3mm to 9mm. The thickness of glass doesnt necessarily mean itll be harder to break. What breaks glass? Force. Force = mass x acceleration. Thicker glass means youll be increasing mass which will increase the overall force. Thicker glass may be more durable to smaller bumps and such, but if it falls or tips theres a greater chance it will break.
People always hit thicker glass tubes and claim that the smoke is smoother. This is true and not true at the same time...more discussed in the next section...
-Outer/Inner diameter of tubing
Most glass tubing used in pieces comes in a standard outer diameter of 50mm. As glass gets thicker, the
outer diameter usually stays fixed and the inner diameter becomes smaller. This is why given two tubes of identical design but differing thickness of glass, the thicker will appear smoother to the user (less volume).
There are glass blowers that use different diameter tubing such as 40mm and also some companies (I know ZOB has done this) produce thicker glass with bored out centers so the smoke volume isnt changed. Ive also heard of glassblowers who work down tubes to make them shorter but thicker. Im not 100% familiar with this process maybe someone can chime in.
-Quality of joint
The ground glass joints featured on these pieces also come in differing quality. This is arguably the most stressful location on the piece. They come in different thicknesses but can roughly be categorized to standard, bistabil (what ROOR uses), and some super thick joints like honalee or "uber"
-14mm vs. 18mm vs. 24mm This refers to the ground glass joint diameter used in pieces. The differences are pretty obvious; an 18mm will clear faster than a 14mm due to increased airflow. Arguably, a 14mm will allow you to produce a more concentrated hit, but this difference is usually not noticeable. 14mm tend to be cheaper than 18mm counterparts. 24mm joints can also be found in some "heavy hitter" pieces. Just like the difference between 14 and 18, a 24 will clear faster than both 14 or 18.
Also, joints come in varying qualities (both the male and female end) so make sure the joints are clean, free of imperfections, and slide easily in/out without much resistance or slack.
-Quality of joint weld
Looking at the joint from top down, look at the thickness of the glass around the joint. I wish I had a picture to point out exactly what Im referring to but look right around the base of the joint (it kind of looks like a large oval when directly looking at the joint from the front of the piece)
-Quality of glass (bubbles)
Check the glass itself to see if there are any air bubbles, especially around key stress points like the joint. These can weaken the structural integrity of the glass
-Lines of tube (make sure everything is perpendicular)
-This might seem like a moot point but Ive seen many beakers and straights that dont sit perpendicular to the bottom. It doesnt really effect smoking dynamics (unless the lean is so bad it throws off the perc water levels) but is indicative of the quality of production
-Ash catcher compatibility (compare joint angles of female piece and male a/c)
-You want to make sure that the reservoir of the ashcatcher sits parallel to the base of the piece to ensure maximum diffusion and minimal splashback
-Try to see if the design of the ashcatcher is tall enough to prevent this, or if there is some type of splash guard integrated into the design
-Large pieces with carbs:
I'm not referring to bubblers and pipes but large glass pieces. Drilling that carb hole jeopardizes the structural integrity of the glass and becomes a super weakspot in the design.
-Type of perc
Percolators serve to break down the smoke into smaller components and forcing them through water filtration again to provide additional filtration and cooling. They come in a variety of designs which all employ the same principle but in many different ways. Off the top of my head (and the designs I understand) I can think of these types of percs: Inline, Tree, Dome, Circulator, and Disc/Natural. I cannot tell you which perc is better than another because a lot of it depends on the design of the particular perc in question
There are common traits in perc's to look for. They typically are the source of most drag in a poorly designed piece. Check the upstem diameter to see that there is enough flow and see how many # of slits are placed (whether it be around the dome or on each arm)
inline/halo: I decided to group halo percs with inline percs as they both force the smoke to travel laterally through diffusion slits (maximizing surface area contact smoke:water ratio). In theory these should filtrate the smoke most (compared to say a "normal #" of tree arms) However ZOB's halo left much to be desired and the Inline designs coming out these days are significantly better in performance.
tree: tree percs work by directing the smoke stream through a upstem which then is forced 180* down back via separate glass arms into another reservoir of water where it is filtrated and continues up the tube. Check to see the # of tubes, how well the joint is that holds all the arms, and the thickness of each tube. There are small differences that can lead to different smoking dynamics such as the # of slits per arm or whether the bottom of the arm is sealed/opened/slit.
dome: dome percs work similar to tree, featuring an upstem that is then covered by a "dome" which has slits on the side. Since the dome is sealed over the upstem (minus the slits) the smoke is force to travel up the upstem and then back down inside the dome and exit out of the slits through water and up the tube. One thing to look for in particular is the distance between the upstem and the top of the dome. I've seen many production pieces that have very little clearance between the upstem and top of the dome, which creates a restriction in air flow, translating into more drag. I believe this is the key weak point in dome percs
circulator: circulators can be considered the latest generation of dome percs. Instead of featuring 4 or 5 slits around the circumference of the dome, these percs feature many tiny slits. This provides more diffusion and with the many # of slits increases the air flow and reduces the turbulence.
disc/natural: these operate by having the water level place below a solid disc with holes cut into (sometimes circular, sometimes triangular). As the vacuum is created when inhaling, it forces both the water and smoke to be sucked up through the holes in the disc as it filtrates. The cool thing about this design is once the entire bowl is milked, since the water level is now above the disc it is very easy to clear with minimal drag. My only complaint I've seen is that sometimes a disc perc by itself is a little chuggy and there is this initial difference in water pressure one must overcome before starting to milk
-Type of downstem
standard downstem: This is your typical downstem that comes stock with most pieces. Just a simple tubing with ground glass joint. It tends to be "chuggy" but usually clears the fastest of all downstems
slit diffused downstem: These are probably the most common type of diffuser downstem. The smoke travels down the tubing like any other downstem but exits the tip of the downstem through small slits cut along the sides. Look at the number of slits, how large the slit is, and how large the hole at the end of the downstem is to get a good idea of its diffusion capability and how draggy it'll be.
german-style diffused downstem : These downstems are also very popular and feature a tip that is pierced with small holes. Sometimes the holes are placed in straight bands around the stem, sometimes randomly, and sometimes as a spiral. They arguably provide better diffusion as the smoke is forced to travel out a greater # of openings but can also add significant drag if not designed properly. Check the # of holes, diameter of hole, and diameter of hole at the very tip to see how draggy it is.
Gridline downstem: Sovereignty has a design they call the "gridline downstem". It's more of a modified german-style downstem as it feature small pierced holes in a grid like fashion on only one side of the downstem. The hole at the end is relatively large to allow for quick clearing.
Gridcap: From my limited experience in hitting a gridcap, I would say it is a mixture of a dome perc and natural perc put together. Instead of a disc with various holes placed on its surface, there is a dome with multiple holes pierced all throughout the dome (around and above). It provides significantly more filtration than a disc perc. I've only seen this incorporated as the initial filtration (in replacement of a traditional downstem). One thing I noticed is there still is that water pressure difference the user needs to overcome before it starts to milk (if you don't understand what I'm saying, think like a few milliseconds of drag as the water levels rise above the dome but then it becomes dragless from that point on forward)
Gridline: These feature a fixed stem style except multiple downstems are placed horizontally across the base of the tube at the same level. Diffusion slits are cut on the top of these downstems. One could think of this as a quasi-inline sort of piece as it forces the smoke to travel laterally. As of now this design is exclusive to Sovereignty glass and I must say it performs very well.
Fixed-Stem: Instead of having one downstem connect the bowl to the base of the piece, these have a tree perc attached to the downstem. As you can imagine, this provides significantly more filtration than a single diffused downstem.
Stemless: These have a straight tube that connects the bowl and bends 90* to connect to the reservoir of the tube. the ground glass joint for the slide is placed above the 90* bend so water levels never interfere with the bottom of the slide. These have that same initial water displacement you have to overcome before a smooth milk, but it clears super fast since. Some companies have placed diffused "caps" over the top of the water level to try to reduce the "chugginess" of the hit
I hope this guide gives you a quick crash course on glass. If you want more information, I suggest you explore
www.glassdistrict.com and research just like you came on this forum to research vaporizers. Looking at glass is addicting