FREQUENTLY ASKED QUESTIONS ABOUT: |
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TYPES OF THIN SECTIONS, THEIR USES AND PREPARATION
CUTTING YOUR OWN BLANKS AND OTHER D.I.Y. PROCEDURES
PETROPOXY 154 Answers to many questions concerning Petropoxy 154, as well as helpful procedural tips, can be found in the pages of the Petropoxy 154 User’s Manual, available for download from this website.
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| What are the differences between the various types of thin sections, and what are they each used for? |
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A Standard thin section is a 30 µm-thick slice of rock, concrete, etc., mounted with epoxy onto a 27 × 46 mm glass slide. Using a grinding process involving flat, horizontal wheels (called lapping), we finish standard thin sections with 600-mesh (extra-fine) silicon carbide abrasive and fit them with thin glass coverslips. This type of thin section is best suited for routine petrography.
We are able to process the surface of a lapped thin section with a series of progressively finer polishing compounds to produce a polished thin section which has a scratch-free, highly reflective surface. Polished thin sections can be used for electron microprobe or SEM analysis, or to identify by reflected-light petrography the various kinds of opaque, metallic minerals present in most rocks. Because these types of analyses require direct access to the sample surface, polished thin sections are not coverslipped. Polished ore sections are ±1 mm thick, polished plates mounted on standard 27 × 46 mm slides for reflected-light microscopic analysis of opaque metallic minerals (ore minerals). The actual thickness of each section may vary -- but we take care to insure that it’s uniform. Doubly-polished thin sections are polished on both sides ... that is, the side of the section mounted to the glass slide -- as well as the facing surface -- is polished. Not only do these sections serve the same purposes as polished thin sections, but they provide a much sharper image under the microscope and therefore allow one to examine intracrystalline structures in much greater detail. Sections prepared for fluid inclusion are usually between 100µm to 200µm thick and are doubly-polished to provide a clear view of internal structures. They are mounted to slides with an acetone-soluble adhesive so they can be removed (we use either cyanoacrylate “Super Glue” or Crystalbond™). Samples are examined for microscopic bubbles inside mineral grains (fluid inclusions) trapped when the mineral formed. These inclusions usually contain a tiny quantity of liquid which represents condensed vapor that formed the bubble. Special microscopes with heated stages are used to heat the sections to the point where the liquid in the bubbles converts back to vapor. By observing this transition under the microscope one can determine the temperature at which the vapor became trapped (usually taken to be the mineral’s formation temperature). TEM thin sections are prepared for “Transmission Electron Microscopy”, a technique designed to analyze intracrystalline structures on a molecular scale. Instead of reflecting a beam of electrons from a polished surface (as in electron microprobe analysis), an electron beam is passed through the sample. There is some difference in opinion as to what type of thin section is best -- standard, polished or doubly polished -- but in any case the section must be somewhat thinner than normal (±20 µm) and mounted with a non-permanent, acetone-soluble adhesive (we use Crystalbond™). The price for non-doubly-polished TEM sections will be considerably less - contact us for a quote. We prepare TEM sections as thin as practical, given the type of material at hand, but TEM analysis normally requires sections to be much thinner than 20 µm. Any further reduction of thickness is usually accomplished by a process called "ion milling", which is beyond our lab’s capabilities. |
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| Do you use water or oil to prepare your thin sections? We prefer to use water whenever we can because it’s less expensive and much less messy! But we will of course use oil to prepare water-sensitive material like sulfates, halides and swelling clays. Please let us know if you suspect the presence of such things in your samples! Everything cut and lapped with oil is cleaned with isopropyl alcohol. All polishing is done with oil, too. |
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| What is the standard thin section thickness? Standard thickness is 30µm (0.03 mm [0.0013 in]). |
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| Why would I need ultrathin sections? Some rocks are so fine-grained that individual crystals my be smaller than 30µm. These tiny mineral grains may overlap each other in a standard thin section and make it difficult distinguish and identify them. An ultrathin (± 15 µm) section would help solve this problem. You can specify whatever thickness you prefer, too. |
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| Can you prepare "thick" thin sections? Does it cost extra? Sections thicker than 30µm are not a problem, and thicknesses up to about 200µm do not cost extra. Just specify the thickness you want as part of your instructions. Sections thicker than 200µm may incur a nominal extra charge. |
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| Can you provide thin sections mounted on quartz slides? Yes, we can prepare thin sections using 25 × 50 mm quartz slides. Quartz slides are quite expensive, however, and will add $20-$25 to the per section cost. |
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| How long does it take to make a thin section? Thin section preparation is a very labor-intensive and time-consuming endeavor where most of the work is best performed by hand. And much of the prep time includes what it takes to dry samples between each step in the process. But even so, a standard thin section of cooperative material can be completed in a single workday without too much trouble. |
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| What are the sizes of slides you provide? Our standard-size thin sections are mounted on 27 × 46 mm petrographic slides. Larger-format (oversize) thin sections are mounted on 51 × 75 mm (2×3") slides. Circular slides, 1" in diameter, are available for polished thin sections for microprobe. Slightly smaller standard petrographic slides (25 × 45 mm), as well as 25 × 75 mm (1×3") slides, are available on request. |
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| The standard-sized polished thin sections you made for us don’t fit the microprobe’s sample holder (they’re too small). What gives? A few customers have had this problem, and we’re not sure why. Most holders should be able to accommodate a slide at least 45 mm long. We recently switched from 25 × 45 mm to 27 × 46 mm slides, so we hope this will no longer be a problem. |
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| How do you label your slides? We scratch the numbers on the back of each slide with a diamond-tipped scribe. If you’d like us to label your slides differently, let us know (there may be a small extra charge). |
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| What do you use to attach coverslips? In most cases we use non-permanent Canada balsam, which makes it easy to remove coverslips if it ever becomes necessary to stain or polish your thin sections at some later date. However we will attach cover slips with epoxy when sample heat-sensitivity precludes the use of Canada balsam, which requires temperatures of up to about 135°C. |
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| Are coverslips absolutely necessary? Yes and no. Even though the lapped surface of a standard thin section may look extremely smooth, on the microscopic level it’s actually riddled with tiny pits and scratches which scatter light in all directions. This produces a dark and indistinct image under the microscope. A coverslip accomplishes two things: 1) the coverslip adhesive fills these pits to produce a brighter and sharper image, and 2) it protects the surface of the section from normal wear and tear. Many customers request no coverslips so they can perform mineral stains or other microchemical tests, but uncovered thin sections will require oil, glycerin, water--something--on the section surface to obtain a decent image under the microscope. |
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| I’d like to remove coverslips from thin sections you made for me. Do I need to send the sections back to you? No, you don’t have to. Simply warm the slides to about 100ºC for a few minutes, either in an oven or on a hot plate, until the Canada balsam softens and the slips can be slid off with a toothpick. Use isopropyl alcohol or acetone to remove balsam residue once the slides have cooled. We’d of course be happy to remove your coverslips if you’d rather we did it. If your sections contain heat-sensitive minerals, or if they were prepared by another lab which affixes coverslips with epoxy instead of Canada balsam, then you will need to send the sections to us to remove them. |
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| What do you use to achieve your final polish? The fourth and final (brief) step in our hand-polishing process is 1/4µm diamond compound on a cloth-covered wheel. |
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| Do you polish with oil, glycol or water? All of our polishing is accomplished with oil. |
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| I’d like to have polished thin sections made from standard thin sections I already have. Can this be done? Usually. Even if your thin sections have "permanent" coverslips affixed with epoxy, they can often be removed without too much trouble. And be aware that polishing removes a certain amount of material, so a 30µm standard thin section is likely to become a 20-25µm polished thin section. |
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| What epoxy do you use to prepare and mount your sections? The epoxy we use most often is Petropoxy 154. It is specifically designed for the preparation of petrographic thin sections, and is far superior to other media we’ve tried. Petropoxy 154 can’t be used for everything, however, so for contrary stuff we use a product called Epo-tek® 301. It is important to note that mixed Petropoxy 154 contains significant amounts of boron and should be avoided when preparing samples that will be analyzed for boron isotopes. Please be sure to let us know if Petropoxy 154 will present a problem for you in this regard. |
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| What are the refractive indices of the various epoxies you use? Petropoxy 154 has a refractive index of 1.540 (hence the name). Epo-tek® 301 is 1.538-1.540, and the Canada balsam we use for coverslips is around 1.52. |
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| What are the cure temperatures of your epoxies? Petropoxy 154 cures at 135°C (~275°F) -- so we can’t use it for heat-sensitive stuff. Epo-tek® 301 will cure at room temperature. Balsam for coverslips requires a temperature of around 120°C. |
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| How do you determine if epoxy impregnation is necessary? Each thin section blank receives a coat of epoxy prior to lapping at no charge. If epoxy soaks into the sample so that we need to apply one or two additional coats, a "light impregnation" charge applies. If your sample is too friable to cut, or is otherwise very permeable, then a "heavy impregnation" charge will apply (see price list for details). Soils and other extremely permeable samples which consume high volumes of epoxy will be charged by the milliliter. |
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| Do you impregnate using vacuum? Sometimes. The epoxies we use are very low-viscosity and penetrate very well, so there’s usually no need for vacuum impregnation. But for very permiable material or blue epoxy impregnation we will sometimes use vacuum for any extra penetration it may provide. |
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| What’s the deal with blue epoxy? Any pore spaces (natural voids) present in samples impregnated with blue epoxy will be bright blue and easy to see in thin section. So, upon request, we will impregnate samples with blue epoxy so that porosity estimates will be much easier to obtain. We take the time to try and fill as many voids as we can so estimates can be as accurate as possible. |
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| What are "sample-determined treatments" and when are they needed? Some samples possess physical or chemical characteristics that may require some special handling at extra cost (see price list for details). Sometimes the need is obvious, as in the case of really friable or permeable things which need some degree of epoxy impregnation to stabilize them (see above). But often the need for special treatments can’t be determined until we actually begin working on the samples. And because we don’t have the ability to know each sample’s “provenance” or “lithologic context”, it’s really important for us to know if you’re aware or suspect the presence of things that require special handling, such as: Heat-sensitive minerals -- most commonly gypsum and sulfur, which we prepare at or near room temperature. |
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| Can you cut thin section blanks from my rocks, or do you only accept precut samples? Sure, we can cut blanks from your hand samples, slabs or cores as part of our service. Sending us precut samples saves us time and you money, though ... and there’s the added advantage of being able to choose the precise area of your samples you’d like to have sectioned. |
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| If I cut my own blanks, what size should they be? Your blanks should be no larger than 24 × 40 × 10-15 mm (45 × 70 × 10-15 mm oversize), and both the front and back sides should be reasonably flat and parallel. Note that the face of each blank should be slightly smaller than the slide -- if your blanks are cut to these dimensions they won’t cause us any time-consuming trouble like cracked or broken glass. We’ll be happy to send you a wood model you can use to compare your blanks to the “ideal” as you’re cutting them. If we need to trim your blanks to size, you will be charged for "cut material". |
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| Should I epoxy-impregnate my samples myself before I send them to you? We really rather you didn’t. There are so many different types of resins and epoxies on the market -- each with its own set of physical properties -- we can’t hope to know how any one of them might behave during the thin sectioning process. We have encountered all sorts of problems with preimpregnated samples, from improperly mixed and poorly cured epoxy to hard resins that will expand or contract enough to crack slides with even slight temperature variations. And in rare cases some stuff can react with the epoxies we use. But if you have your heart set on stabilizing samples yourself, please consider using what we do* -- or at least send along as much information as possible about the particular medium you chose so we can adjust our procedure accordingly. Expect extra charges for any trouble we may encounter. *(Click here for information about Petropoxy 154). |
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| Does it help if I lap my blanks smooth before I send them? Not really. Lapping blanks is a critical step in the process and has a direct effect on the quality of the finished thin section. It requires lapping wheels that are maintained precision flat at all times, and sample surfaces that are stabilized with epoxy to prevent possible disintegration. It also takes some skill to recognize a sufficiently-lapped surface that’s ready for mounting. So even when we receive pre-lapped blanks we will impregnate and lap them anyway, just to be safe. |
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| How large a hand sample do you need? A chunk about the size of your fist is plenty big enough. Anything larger runs the risk of incurring sawing charges (see "Sample-determined Treatments" above). |
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| How small is "too small"? We have prepared standard thin sections of single grains smaller than 1 mm, and polished probe mounts of single grains embedded in epoxy as small as 125µm. |
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| Do I have to fill out one of your order forms? No, order forms are not mandatory. Our forms are designed to make it easy for you to provide all the information we may need, but a letter with clear instructions and a sample list -- as well as billing and shipping information -- will do just as well. In any case, please be sure the return shipping address you provide is accurate and appropriate -- private carriers such as UPS, FedEx, etc., will not deliver to P.O. Boxes or other “U.S. Mail only” addresses. |
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| How should I prepare my samples for shipping? A lot depends on the type of samples you send, but the main thing is to clearly label them. It’s best if you can place each sample in its own bag or container with the sample number written on the outside. Or you can write the number --in non water-soluble ink!-- either directly on the sample itself (or on a piece of masking tape wrapped around it, material permitting). Even better if you do both. Use a sturdy shipping container, wrap samples individually, and/or pack spaces between them with plenty of newspaper, packing peanuts, etc., so they don’t knock around when you shake the box. If your samples are friable or fragile, wrap and pack them with more appropriate amounts of cushioning material -- but please don’t go overboard! It can take a lot of time to de-construct all the tape, twine and tissue paper sculptures you create wrapping up your stuff! |
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| What instructions do I need to provide? Include a sample list with your package and let us know the type(s) of thin section and any optional treatments you would like (one of our order forms is handy for this). If it matters, let us know where you’d like us to cut your samples. If you’re sending precut blanks, indicate which side you’d prefer mounted to the slide, either by writing "mount opposite side" directly on the blank, or including an instruction like "mount side opposite label", etc., in your letter or on the order form. It helps to tell us if there’s anything specific you’re hoping to see in your sections, too. Be sure to provide contact information--phone, fax, email--in case we have any questions, and include any billing info we may need (i.e., billing contact person, correct billing address, purchase order or credit card number). Make sure the return shipping address is complete and correct. |
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| Do I need to use a specific carrier? No, we’re serviced by everyone: UPS, FedEx, US Mail -- use whomever is most convenient for you. |
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| Do you provide any discounts? We don’t offer any discounts per se, but you can lower the cost of your thin sections significantly by providing us with cut samples. You receive a discount if you send us rocks with one or more sawn surfaces (like slabs and cores). We offer an even greater discount if you send precut thin section blanks that are no larger than 24 × 40 × 10-15 mm (45 × 70 × 10-15 mm oversize). Large orders of 100 or more samples also qualify for a volume discount. And you can also save if you don’t want coverslips on your standard thin sections. Please see our current price list for details. |
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| How should I pay for my order? US customers may pay by check (made out to "BurnhamPetrographics LLC"), money order, Visa, Mastercard, Discover and American Express (personal checks are OK). We urge customers outside the US to pay by Visa or Mastercard (if possible), or by US Dollar International Money Order. Otherwise, all check payments must be in US dollars drawn on a US Bank (with US micro transit code), and the payment total presented to the issuing bank must be increased by the amount of any and all transaction fees which are imposed and deducted from the check by the bank. Please make checks payable to "Burnham Petrographics LLC". We also accept Bank Wire Transfers, but we must add $40 to the cost of your order to cover fees imposed by banks at both ends of the transfer. |
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| Do you accept purchase orders? Yes, we welcome purchase orders. |
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| My Petropoxy 154 Curing Agent has become very thick--almost solid--and/or is a different color than I’m used to. Has it gone bad? Do I need to replace it? No, there is nothing wrong with your Curing Agent. The color of the product usually varies somewhat from batch to batch, but has no bearing on quality or effectiveness. And even though it doesn’t happen all the time, it is completely normal for Petropoxy 154 Curing Agent to crystallize or solidify -- especially when it’s stored below room temperature. It is easily returned to it’s original liquid form by heating, either in a microwave or conventional oven, without any deleterious effects. Please refer to page 9 of the Petropoxy 154 User’s Manual for this restoration procedure. |
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| What is the shelf-life of unmixed Petropoxy 154? How long will it last? Petropoxy 154 Resin and Curing Agent have indefinite shelf-lives. Keep their containers tightly closed in a cool, dark place and both should last for many years. |
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| Is Petropoxy 154 compatible with all sample types? Petropoxy 154 is an excellent medium for preparing thin sections of the vast majority of materials, but not everything. Because Petropoxy 154 requires heat (135°C) to cure, it can’t be used on heat sensitive things like gypsum and sulfur. Chloride ions interfere with Petropoxy 154’s cure reaction, so it can’t be used on halite or other soluble halides containing chlorine. Some very fine powders also seem to interfere with the cure reaction. And there have been some reports that Petropoxy 154 will attack and dissolve coccoliths. It’s important to note that mixed Petropoxy 154 contains a significant amount of boron, so it should not be used at all if you are preparing samples that will be subsequently analyzed for boron isotopes. |
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I can’t get my mixed Petropoxy 154 to cure completely. What’s wrong?
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| I have run out of curing agent, but still have some resin. How come? We fill bottles and jars with slightly more product than is indicated on their labels, and often there’s more extra resin than curing agent. And by the way, it’s OK to use a bit less curing agent -- you can use as little as 5 pph (i.e., 0.5 ml/10 ml resin) without adversely affecting cure or cured properties of Petropoxy 154. |
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| Can we buy slide boxes from you? We don't carry slide boxes anymore, unfortunately. Cardboard boxes for 25 standard-size slides are available at Beta Diamond Products info@betadiamond.com and perhaps elsewhere. The 100-capacity sturdy wood-frame boxes (with plastic inserts) are no longer being manufactured. |
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| Do you sell thin section sets for classroom use? We can put together an impressive set of thin sections from samples of all rock types, as well as minerals. Let us know your needs and we’ll be happy to put together something for you! |
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| Do you offer petrographic analyses as part of your service? Most of our customers prefer to perform their own analyses, but once in a while we are asked to provide a rock name and/or modal analysis, or carry out simple point-counts for porosity estimates, among other things. We’re happy to do this -- if we have the time(!) Contact us for more info. |
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| What is your average turnaround time for "Standard" service? As news of our good work spreads -- and more people send us more work -- our standard turnaround time has been steadily increasing. It’s becoming more and more difficult to provide reliable standard turnaround estimates, and whatever we say is often valid only until the next UPS or Mail delivery! It is likewise difficult to come up with an average turnaround time for standard orders, but given our recent circumstances a wait of several months is possible throughout the year. Some of the things that contribute to such long waits are the number of Rush, Priority or Standard-Plus orders we receive, larger-than-normal backlog, orders with large numbers of samples, or material that is technically difficult and time-consuming to prepare--things that for the most part are outside our control. Please let us know if you are working under a deadline ... sometimes we are able to perform a kind of "triage" based on deadlines in an effort to return everyone’s sections when they need them. But if you absolutely need your order finished in less than 6-8 weeks, we strongly urge you to consider either our "Standard Plus" or "Priority" service -- the cost is higher, but you’ll be sure to have everything back in plenty of time. Expedited service is subject to availablity, however. See our Order Forms page and/or our price list for details. |
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| Do you have a busy season? Business is fairly moderate throughout the year, but Fall through early Winter (after the field season) can be much busier than normal. The flow of samples usually eases up a little in early Spring. |
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| Are your Rush, Priority and Standard Plus turnaround times guaranteed? No, because there are too many factors beyond our control that can increase turnaround time, such as our backlog, order sizes and difficulty, etc. We make every effort to complete orders within the advertised time frames, but because of the overwhelming number of requests for expedited turnaround we’ve received in recent years it has become necessary to place limits on the number of faster turnaround orders we accept so that we can keep our backlog and workflow manageable. That’s why we’re now asking customers to contact us ahead-of-time before sending any samples for faster turnaround. Please see our Order Forms page for more information. |
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| Does your turnaround include transit time? No, so if you’re under a deadline be sure to take into account the day(s) it will take for your package to go from you to us and back again. |
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| ANY OTHER QUESTIONS? Don’t hesitate to ask! Email us at artisans@burnhampetrographics.com or call 1-800-772-3975 | |
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