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Please note that the use of the name "KIRK STIEFF" really only applies to the patterns introduced AFTER 1979. The KIRK name stayed on the KIRK patterns produced by KIRK STIEFF and the STIEFF name stayed on the Stieff patterns.

Calling a 1950's piece of silver KIRK STIEFF is like calling a 1952
Nash Rambler a Chrysler Rambler because Nash became American Motors.. and they were bought by Chrysler in 1983. The same applies to silver.  We call the silver  by the name hallmarked on the silver.. not by a later name. To do otherwise is disrespectful of the American workers that made those pieces of silver so many years ago.

After 1980, KIRK STIEFF did use a shared knife blade that said KIRK STIEFF... and it appeared on both the Kirk and Stieff pattern knives... but the rest of the flatware (forks, knives, etc.) kept the names intact. 

(the PLURAL 
S. Kirk & Sons only applies to 1861-1868 Coin Silver pieces)
When dating the silver of S. Kirk & Son there are several things to keep in mind: 
FIRST, please remember that  S. Kirk & Son did NOT use date marks on the silver. The dating is done by close examination of the type of silver and small changes to the hallmarks. The marks are mostly the same on flatware and hollow ware, with an exception noted below.
SECOND,   S. Kirk & Son FIRST used the word STERLING in 1914.  Earlier pieces have 925/1000.
HUGE >>>>>  The hallmark  "S. KIRK & SON"  has been used TWICE in the companies history...1868-1896 and again 1932-1979.
 A common error is seeing the S. Kirk & Son mark and assuming it is 19th century silver.  If you see the word STERLING and the hallmark S. Kirk & Son the piece is 1932 or newer. (see below)
PLEASE READ THIS.... A very popular on-line silver mark identification site leaves out this valuable information and there is a lot of incorrectly dated Kirk silver on ebay and elsewhere because of it. That site only shows the marks up to 1932 and does not mention the re-use of the old hallmark again starting in 1932
COIN SILVER Kirk made COIN silver from the early days of 1815 and into 1896. They did not start making 925/1000 silver (Sterling) until the mid 1880s. The coin silver will be marked either 11OZ or 10.15 which often shows up as 1015 due to the dot being worn off.  This is not 925/1000 (Sterling) silver. Silver is weighed in TROY ounces, not US ounces as most Americans are used to.   11OZ means the silver is  .9166 percent pure silver.    A mark of     10.15 silver is .896 pure silver. Again... Sterling is .925 
Coin silver was made from ... COINS, that were melted down and remade into silverware and hollow wares.  We lost a lot of American history when much of the old coin silver flatware was "traded in" when Sterling Silver was bought. The coin silver was melted and pure silver added to bring it up to the .925 standard of sterling.  

The White House traded in various odd pieces of silver when the Cleveland administration wanted new silver in the early 1890's.  S. Kirk & Son made the new silver for them. (Kirk recreated the pattern in 1952 for the White House and in 1992  KIRK STIEFF again recreated the 1892 pattern as replacement pieces were needed)
When did Sterling Silver start in Baltimore...  Most silversmiths on the East Coast of the United States started making 925/1000 sterling silver about 1861. This is when the huge silver strikes found in Nevada in 1859 starting making it's way to the east coast of America. This was also the start of the Civil War, so not much silver was produced at this time.  As stated above, Kirk did not start making this finer silver until the mid 1880's. American silver was often considered..."Not as good as european silver" as it was was not sterling. Gotham and Tiffany were making Sterling Silver to match the europeans.  Other American silversmiths eventually were seeing business go to other silversmiths and had to start making finer silver to keep the business running. Much of the older coin silver has been melted down over the years as older sets were traded in for new more fashionable Sterling Silver.
Another common error in selling the silver of S. Kirk & Son is the use of the PLURAL of SONS.  The name was only in use as S. Kirk & Sons from 1861-1868.  In 1861 a second Kirk son joined the firm and in 1863 an third son. By 1868 the newer sons had left the firm and the company went back to the name S. Kirk & Son.
Concerning the FLATWARE pattern Repoussé.   This pattern was introduced in 1845 and in NOT 1828 as commonly mentioned. The HOLLOW WARE pattern REPOUSSÉ was introduced in 1828 with the flatware pattern following almost two decades later.    
The oldest of the Kirk Silver has what are known as ASSAY marks. Baltimore at one time required that all silver be examined by the Assay Office for purity to make sure the public was not being cheated. The Assay mark would be put on the silver to prove its value. This practice ended in 1830 so very little of it still exists.   (see Assay marks  on the charts below)
At the bottom of this guide are photos of  "The History of the House of Kirk" from 1914 with examples of the early assay marks and of the early KIRK hallmarks that can be used to determine the age of the early silver. I caution you to use the info carefully and to fully examine the marks as TINY changes in the marks can change the age by a decade or more. Please keep a close eye on the exact shape of the "&" as that is often the clue you are looking for. 
*COIN silver from S. Kirk & Son from 1846-1861 has a special mark... different from later coin silver after 1868. Refer to the pages posted below to see the mark. The "&" is  different than the later mark. The early "&" is a bit fancier. You have to look close to see the difference.
*COIN silver from S. Kirk & Sons is 1861-1868   (note that this is the PLURAL version) 
*Coin silver from S. Kirk & Son (singular) will be 1846-1896  (Again, please reference the marks to determine if your silver is from the SONS period of 1846-1861. This silver would be rare, but it does appear from time to time.) 
*925/1000  silver from S. Kirk & Son will be mid 1880s-1896  (again, the mark is 925/1000 and NOT the word STERLING) The name changed to S. Kirk & Son Co. in 1896.
* Silver marked S. Kirk & Son CO. was made from 1896-1924. Keep in mind the STERLING mark is 1914 or later. Earlier pieces say  925/1000.  The pieces made about 1914-17 sometimes have both marks
*FLATWARE in the period 1896-1914 has DIFFERENT marks than the HOLLOW WARE. (see below)
*Silver from S. Kirk & Son INC. is from 1924-1932 and is marked STERLING
*Silver from 1932-1979 will say S. Kirk & Son STERLING and is a reuse of the old mark. 
MUCH CLEARER, detailed images of the pages above can be found at website THESTIEFFCOMPANY (INSERT DOT COM) Look in the section on KIRK silver. The site is an educational free site dedicated to research of Baltimore Silver.  Questions can also be emailed to and answered by the sites author.
The hallmark of S. Kirk & Son did not change from 1932-1979.  In 1979 S. Kirk & Son was acquired by The Stieff Company.  The name of the combined company changed in 1980 to The Kirk Stieff Company. The Kirk workers were moved to the Stieff Building in 1980. 
Kirk Stieff was sold to Lenox in 1990. Lenox sold the brand name Kirk Stieff to Lifetime Sterling in 2007. They now make only a few patterns of Kirk silver. No HollowWare has been made since 1999 when Lenox shut down the factory in Baltimore. 
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