Introduction

This is the second in a line of articles where I hope to provide data for the prospective airbrush purchaser that covers key features, evaluates performance using modeling paints and materials, and describes how that performance was measured. I will continue to use standardized products and methods in order to provide situations that can be duplicated by any individual who chooses to do so. From there they can decide what value to place on the information provided.

I have used airbrushes in modeling for about 30 years and I have no affiliation whatsoever with any airbrush, paint or model company. Most of the brushes I evaluate will be brushes that I bought and paid for out of my own pocket. None were received for review or were bought at a discounted rate from a manufacturer for consideration. The ones I don’t personally own, were borrowed from a friend who tolerates my curiosity.

The HOW

I will use two readily available modeling paints using thinners manufactured by the companies who produce and sell the paint. This not an attempt to call into question the suitability of various thinners others use, and there will undoubtedly be people who can achieve better results with their preferred thinner, but these products provide control factors which provide stable and repeatable methods. The paints used will be Tamiya and Vallejo Model Air. They are readily available via the internet even if they are not in your local hobby shop.

Paints will be applied to sheet styrene using the pressures where best performance for the brush in use is achieved for stated thinning ratios. Lines and spray patterns will be measured using digital calipers, so very slight differences will show in metric conversions as they will be taken from the caliper and not from direct conversion of a number. In my opinion, .01” gives a more concrete measurement than .01034” so I won’t go past 3 decimal places. The compressor I use will always have an adjustable and regulated air supply with moisture traps in line between the compressor and the airbrush.

Below are the criteria that I intend to use for all airbrushes I evaluate:

Objective Criteria:
Brand, action type, feed type, trigger type, nozzle type, nozzle size, air fitting size, cup volume, length, diameter and price.

Special Features & Accessories:
i.e. MAC valve, solvent proof seals, preset handle, lids, wrenches, water traps, etc.

Subjective Criteria:
Atomization, ergonomics, fit, finish, pattern size, smoothness of action, ease of cleaning, parts availability.

HP-B PLUS Details and Features

Pic 1. The Iwata HP-B Plus is an upgraded version of one of the world’s most recognizable designs. This family of brushes has been around for decades and has been a proven performer in the illustration and fine art worlds. It is a double action, internal mix, gravity feed design which uses the standard top mounted trigger setup. External surfaces are covered in a tough chrome finish that is basically flawless. The brush uses the standard 1/8” airline fitting like the ones used by Grex, Tamiya, Creos or Harder & Steenbeck brushes. Users with Paasche, Badger or Thayer & Chandler hoses will need appropriate but readily available adapters. The HP-B Plus features a 1/16th oz. color cup, an adjustable trigger assembly, adjustable needle stop and a solvent proof needle bearing. The common street price for the brush is from $190-$220 US dollars.

This airbrush utilizes a small .2mm screw in type nozzle with larger threads than the standard HP-B and is made of fairly tough alloy. The HP-B Plus is roughly 5.8” (14.7 cm) long with a .431” (10.94 mm) diameter main body.

Here is a picture of the standard breakdown of the brush. Pic 2.

The EVALUATION

Physical Details
The mechanical fit of all components used is very good. Most threaded surfaces are chromed though some are in natural brass. The finishing of most internal parts is chrome and polished to a very high level. This which produces a silky smooth feel which inspires confidence from the first touch. The exterior has a flawless chrome finish as would be expected of a brush with a suggested retail of $250.

The balance and weight of this airbrush is very good. There is a cutaway area that allows you to access the needle checking assembly to clear clogs more effectively than with the trigger. Pic 3. This cutaway is convenient at times but the area can create a spot where your hand can press against needle chuck and create friction when the trigger is moved. Undoubtedly, this will vary based on hand size, but for me it does occur. The trigger tension can be adjusted via moving the spring guide and is extremely smooth and very responsive. Whether you prefer a stiff pull or a soft, you can easily get to a comfortable setting and move on. The HP-B Plus has an ungraduated needle stop which is a good feature when you’ve got a lot of time invested in a model and you don’t want to chance pulling back too far on the trigger and ruining your work. It allows you to pre-set your spray pattern for maximum width and repeat it continuously for as long as you need to. Be aware, the needle stop does move very easily, so if you bump the rear of the brush, ensure you check the spray pattern before restart of spraying on your project. The 1/16th oz. color cup is totally in keeping with what is needed for a detail airbrush. It holds enough paint to do brush appropriate functions and doesn’t obscure the sight line when performing delicate work.

The HP-B Plus’s needles and nozzles are small and easily lost but are surprisingly rugged. Pic 4. They are also well machined and very smoothly finished. The brush also features a removable air cap that allows spraying very close to the surface being painted. Pic 5. Exercise extreme care if you choose to do so, as the needle is very easy to damage if you touch the surface being painted. Replacements are readily available but can be somewhat expensive when compared to some other airbrushes on the market. Should you damage these items the cost for both replacements together will run between $35 and $45. With normal use and care, I have only had to replace one nozzle and two needles in this type brush in the past.

The HP-B Plus comes with a 5 year warranty against manufacturing defects. Items that wear beyond useful limits are replaced under this warranty and Iwata-Medea offers a repair cleaning and service which is available for $25.00 if needed. Any replacement parts used in the repair and not covered under the manufacturing defect statement are charged to customer.

In Use Results
The Iwata HP-B Plus is definitely considered a detail airbrush. Its .2mm tip is regularly used by those who are pre- or post-shading a model, spraying free hand camouflage at low pressures or airbrushing highly thinned paints or inks for area washes, weathering or filters. While it can be used for applying paint to larger areas, it will require more coats of paint and it will require substantial patience to get solid coverage when compared to the general purpose brushes with larger tips. It is not intended for broad even coverage, but for very fine atomization. With that being said, a little paint goes a long way with this brush.

The first paint used to evaluate the brush’s performance was Vallejo Model Air. Pic 6. This paint is packaged in dropper type bottles and is advertised by the company as being “airbrush ready”. The paint was shaken well, put into the color cup and sprayed unthinned onto a piece of clean Evergreen sheet styrene. The Vallejo paint sprayed with a somewhat grainy pattern when covering larger areas. Pic 7. This indicated less than optimal atomization, so I experimented with variations in pressure to ensure best performance. Best atomization of the unthinned paint through the HP-B Plus was achieved at a very surprising 15-18 PSI (1-1.25 bar). I definitely expected the thicker material to need more pressure. At this setting, the brush consistently sprayed patterns of 5/32” (4 mm) with minimal overspray, but it still displayed a slightly grainy spray pattern. Overspray increased dramatically when lines above this size were attempted. The smallest lines achieved without thinning were .01” (.26mm) and were achieved at the same pressure. Tip dry was a huge issue when spraying Vallejo Model Air unthinned. Maintaining consistent performance was a chore, as spraying more than 2-3 seconds would cause degradation of spray pattern. Pressure changes did not improve this situation.

The airbrush was cleaned and a new Vallejo Model Air mixture thinned 3 parts paint to 1 part Vallejo 71.161 Airbrush Thinner. Pic 8. With this mixture, the HP-B Plus still sprayed best at 15-18 PSI (1-1.25 bar). The wide spray pattern was only 1/8” (3mm), but the amount of overspray and graininess was much less. Pic 9. The fine line work with this mixture was improved, achieving unbroken lines of .008” (.19mm) without a large amount of tip dry. Clearly, and as expected, the .2mm tip performed better with thinner paint. I did try thinning the Vallejo and dropping the pressure more, but the paint lost its consistent spray pattern and controllability.

The next paint I used to evaluate the HP-B Plus’s performance was Tamiya’s standard acrylic line. Pic 10. Tamiya’s paint is not “airbrush ready”, so I thinned the initial batch 1 part paint to 1 part thinner. This 50/50 ratio is a common mix recommended by Tamiya when using their X-20A thinner, so I used it as a starting point with the Tamiya’s yellow top lacquer thinner as well. Pic 11. I use both of these thinners when spraying Tamiya paints since there are times when I want more “bite” than the X-20A will produce, such as when spraying base coats or on bare plastic. I use X-20A when I need to lay acrylics over enamels without damaging the base coat. I use the same thinning ratios regardless of which Tamiya thinner is used. The 50/50 mix sprayed well with good atomization at 10-13 PSI (.7-.9 bar) but displayed substantial tip dry. Pic 12. The airbrush produced a consistent 5/32” (4mm) spray pattern which was easy to maintain but had a large amount of overspray. Fine line work yielded a .014” (.35mm) line that was repeatable, with good color saturation, but when pressure was pushed higher or lower, the results became inconsistent.

Increasing the ratio of thinner to paint to 2 parts thinner to 1 part paint yielded much better performance. This mixture is pretty close to the famous “thin to the consistency of skim milk” recommendation that most airbrush users are familiar with. I was still able to produce a repeatable 3/32” (.38mm) wide spray pattern, but the atomization was substantially better than with the 50/50 mix and very good by any standard. Pic 13. Fading and shading were seamless and fine lines of .01” (.24mm) could very easily be maintained and repeated at pressures between 9-12 PSI (.6-.8 bar) without tip dry. I have included a close-up picture of the atomization pattern produced by the HP-B Plus so you can see what I mean when I say very good atomization. Pic 14. Additional thinning of the paint is possible on primed surfaces, but thinning the paint more resulted in spider webbing and uncontrollable lines since I was painting on bare plastic.

Cleaning
For the cup cleaning step, I emptied the reservoir, filled the cup with appropriate thinner, and used an old paint brush to swab the cup and get into the recessed area behind the nozzle inside the color cup. I sprayed until the output of the brush was clear and then followed up with a lint free wipe to finish the color cup. The needle was then removed and a solvent soaked interdental brush was run into the needle bearing to remove any debris that might be pulled back into it when the needle was removed. If you follow this procedure, cleaning the brush takes less than two minutes and the brush works fine. I used to take the airbrush completely down after each use, but I did a test several years ago, over a two month period, with several of my brushes and found that my old way of cleaning caused more problems with airbrush performance than this method. During that test I found that as long as I didn’t let paint dry in the brush, I got better and more consistent performance from the wipe and spray over the teardown method; I also damaged far less parts! I’m not suggesting that you change what works for you, but if you are ordering replacement parts for your brush, 9 out of 10 times it’s not because they are worn out, it’s because you damaged them while cleaning your brush.

CONCLUSION

The Iwata HP-B Plus is a superb airbrush. It offers first rate atomization with properly thinned media, excellent detail potential with model paints, good ergonomics, good parts availability, and a solid warranty. If you are in the market for a detail airbrush, I would highly recommend you include this airbrush in your consideration. Next up is another detail brush: the Tamiya HG Superfine…

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